Atoms, Ions, and the Periodic Table What is an atom? It is smallest particle of an element that retains the elements properties. But how did we come to know all the information we have about these tiny particle?

Democritus ( BC) Matter is made of tiny, solid, indivisible particles which he called atoms (from atomos, the Greek word for indivisible). Matter is made of tiny, solid, indivisible particles which he called atoms (from atomos, the Greek word for indivisible). Different kinds of atoms have different sizes and shapes. Different kinds of atoms have different sizes and shapes. Different properties of matter are due to the differences in size, shape, and movement of atoms. Different properties of matter are due to the differences in size, shape, and movement of atoms. Democritus’ ideas, though correct, were widely rejected by his peers, most notably Aristotle ( BC). Aristotle was a very influential Greek philosopher who had a different view of matter. He believed that everything was composed of the four elements earth, air, fire, and water. Because at that time in history, Democritus’ ideas about the atom could not be tested experimentally, the opinions of well-known Aristotle won out. Democritus’ ideas were not revived until John Dalton developed his atomic theory in the 19th century! Democritus’ ideas, though correct, were widely rejected by his peers, most notably Aristotle ( BC). Aristotle was a very influential Greek philosopher who had a different view of matter. He believed that everything was composed of the four elements earth, air, fire, and water. Because at that time in history, Democritus’ ideas about the atom could not be tested experimentally, the opinions of well-known Aristotle won out. Democritus’ ideas were not revived until John Dalton developed his atomic theory in the 19th century!

John Dalton ( ) All matter is composed of extremely small particles called atoms. All matter is composed of extremely small particles called atoms. All atoms of one element are identical. All atoms of one element are identical. Atoms of a given element are different from those of any other element. Atoms of a given element are different from those of any other element. Atoms of one element combine with atoms of another element to form compounds. Atoms of one element combine with atoms of another element to form compounds. Atoms are indivisible. In addition, they cannot be created or destroyed, just rearranged. Atoms are indivisible. In addition, they cannot be created or destroyed, just rearranged.

Dalton’s theory was of critical importance. He was able to support his ideas through experimentation, and his work revolutionized scientists’ concept of matter and its smallest building block, the atom. Dalton’s theory was of critical importance. He was able to support his ideas through experimentation, and his work revolutionized scientists’ concept of matter and its smallest building block, the atom. Dalton’s theory has two flaws: Dalton’s theory has two flaws: In point #2, this is not completely true. Isotopes of a given element are not totally identical; they differ in the number of neutrons. Scientists did not at this time know about isotopes. In point #2, this is not completely true. Isotopes of a given element are not totally identical; they differ in the number of neutrons. Scientists did not at this time know about isotopes. In point #5, atoms are not indivisible. Atoms are made of even smaller particles (protons, neutrons, electrons). Atoms can be broken down, but only in a nuclear reaction, which Dalton was unfamiliar with. In point #5, atoms are not indivisible. Atoms are made of even smaller particles (protons, neutrons, electrons). Atoms can be broken down, but only in a nuclear reaction, which Dalton was unfamiliar with.

Discovery of the Electron JJ Thomson ( ) Discovered the electron, and determined that it had a negative charge, by experimentation with cathode ray tubes. A cathode ray tube is a glass tube in which electrons flow due to opposing charges at each end. Televisions and computer monitors contain cathode ray tubes. Discovered the electron, and determined that it had a negative charge, by experimentation with cathode ray tubes. A cathode ray tube is a glass tube in which electrons flow due to opposing charges at each end. Televisions and computer monitors contain cathode ray tubes. Thomson developed a model of the atom called the plum pudding model. It showed evenly distributed negative electrons in a uniform Thomson developed a model of the atom called the plum pudding model. It showed evenly distributed negative electrons in a uniform positive cage. Diagram of plum pudding model: Diagram of plum pudding model:

Discovery of the Nucleus Ernest Rutherford ( ) Discovered the nucleus of the atom in his famous Gold Foil Experiment. Discovered the nucleus of the atom in his famous Gold Foil Experiment. Alpha particles (helium nuclei) produced from the radioactive decay of polonium streamed toward a sheet of gold foil. To Rutherford’s great surprise, some of the alpha particles bounced off of the gold foil. This meant that they were hitting a dense, relatively large object, which Rutherford called the nucleus. Alpha particles (helium nuclei) produced from the radioactive decay of polonium streamed toward a sheet of gold foil. To Rutherford’s great surprise, some of the alpha particles bounced off of the gold foil. This meant that they were hitting a dense, relatively large object, which Rutherford called the nucleus.

Rutherford then discovered the proton, and next, working with a colleague, James Chadwick ( ), he discovered the neutron as well.

Models of the Atom - Niehls Bohr Developed the Bohr model of the atom (1913) in which electrons are restricted to specific energies and follow paths called orbits a fixed distance from the nucleus. This is similar to the way the planets orbit the sun. However, electrons do not have neat orbits like the planets. Developed the Bohr model of the atom (1913) in which electrons are restricted to specific energies and follow paths called orbits a fixed distance from the nucleus. This is similar to the way the planets orbit the sun. However, electrons do not have neat orbits like the planets. Diagram of Bohr model: Diagram of Bohr model:

Quantum Mechanical Model This is the current model of the atom. We now know that electrons exist in regions of space around the nucleus, but their paths cannot be predicted. The electron’s motion is random and we can only talk about the probability of an electron being in a certain region. This is the current model of the atom. We now know that electrons exist in regions of space around the nucleus, but their paths cannot be predicted. The electron’s motion is random and we can only talk about the probability of an electron being in a certain region.

Sub-Atomic Particles Each atom contains different numbers of each of the three SUBatomic particles ParticleSymbolCharge Molar Mass Where found Proton p+p+p+p Nucleus Neutron n0n0n0n Nucleus Electron e-e-e-e Electron Cloud “A neutron walked into a bar and asked how much for a drink. The bartender replied, “For you, no charge.”

Atomic Number The periodic table is organized in order of increasing atomic number. The atomic number is the whole number that is unique for each element on the periodic table. The atomic number defines the element. For example, if the atomic number is 6, the element is carbon. If the atomic number is not 6, the element is not carbon. The atomic number represents: the number of protons in one atom of that element the number of protons in one atom of that element the number of electrons in one atom of that element (with an ion, the electrons will be different) the number of electrons in one atom of that element (with an ion, the electrons will be different) **Therefore, protons = electrons in a neutral atom**

Atomic Mass mass of an element measured in amu (atomic mass units) mass of an element measured in amu (atomic mass units) all compared to C-12 (the mass of carbon 12, which has a mass of exactly 12 amu all compared to C-12 (the mass of carbon 12, which has a mass of exactly 12 amu listed on the periodic table listed on the periodic table Mass number= #of protons + # of neutrons Mass number= #of protons + # of neutrons

Isotopes Isotopes are atoms of an element with the same number of protons but different numbers of neutrons. Isotopes are atoms of an element with the same number of protons but different numbers of neutrons. Most elements on the periodic table have more than one naturally occurring isotope. Most elements on the periodic table have more than one naturally occurring isotope. There are a couple of ways to represent the different isotopes. One way is to put the mass after the name or symbol: Carbon-12 or C-12 There are a couple of ways to represent the different isotopes. One way is to put the mass after the name or symbol: Carbon-12 or C-12 Another way is to write the symbol with both the mass number and atomic number represented in front of the symbol: Another way is to write the symbol with both the mass number and atomic number represented in front of the symbol:

Determining Average Atomic Mass The atomic mass on the periodic table is determined using a weighted average of all the isotopes of that atom. The atomic mass on the periodic table is determined using a weighted average of all the isotopes of that atom. In order to determine the average atomic mass, you convert the percent abundance to a decimal and multiply it by the mass of that isotope. The values for all the isotopes are added to together to get the average atomic mass. In order to determine the average atomic mass, you convert the percent abundance to a decimal and multiply it by the mass of that isotope. The values for all the isotopes are added to together to get the average atomic mass.

Example of Average atomic mass calculation Given: 12 C = 98.89% at 12 amu 13 C = 1.11% at amu Calculation: (98.89%)(12 amu) + (1.11%)( amu) = (0.9889)(12 amu) + (0.011)( amu) = amu

Now you try one: Neon has 3 isotopes: Neon-20 has a mass of amu and an abundance of 90.51%. Neon-21 has a mass of amu and an abundance of 0.27%. Neon-22 has a mass of amu and an abundance of 9.22%. What is the average atomic mass of neon? Neon has 3 isotopes: Neon-20 has a mass of amu and an abundance of 90.51%. Neon-21 has a mass of amu and an abundance of 0.27%. Neon-22 has a mass of amu and an abundance of 9.22%. What is the average atomic mass of neon? The answer is: The answer is: (0.9051)( amu) + (0.0027)( amu) + (0.0922)( amu) = amu Now compare this mass for Neon to the mass on the periodic table!

Electromagnetic Radiation Electromagnetic radiation is a form of energy that travels through space in a wave-like pattern. eg. Visible light Electromagnetic radiation is a form of energy that travels through space in a wave-like pattern. eg. Visible light It travels in photons, which are tiny particles of energy that travel in a wave like pattern. Although we call them particles, they have no mass. Each photon carries one quantum of energy. It travels in photons, which are tiny particles of energy that travel in a wave like pattern. Although we call them particles, they have no mass. Each photon carries one quantum of energy. These photons of energy travel at the speed of light (c) = 3.00 x 10 8 m/s in a vacuum These photons of energy travel at the speed of light (c) = 3.00 x 10 8 m/s in a vacuum

What is a wave and how do we measure it? Frequency (ν) – number of waves that passes a given point per second (measured in Hz) Frequency (ν) – number of waves that passes a given point per second (measured in Hz) Wavelength (λ) – shortest distance between two equivalent points on a wave (measured in m, cm, nm) Wavelength (λ) – shortest distance between two equivalent points on a wave (measured in m, cm, nm)

Electromagnetic spectrum (EM) The electromagnetic spectrum shows all wavelengths of electromagnetic radiation – the differences in wavelength, energy and frequency differentiates the different types of radiation. The electromagnetic spectrum shows all wavelengths of electromagnetic radiation – the differences in wavelength, energy and frequency differentiates the different types of radiation. Note that as the wavelength increases, the energy and the frequency decrease. Note that as the wavelength increases, the energy and the frequency decrease.

Ground state vs. Excited state Electrons generally exist in the lowest energy state they can. We call this the ground state. Electrons generally exist in the lowest energy state they can. We call this the ground state. However, if energy is applied to the electrons, they can be “excited” to a higher energy and we call this an excited state. However, if energy is applied to the electrons, they can be “excited” to a higher energy and we call this an excited state. The excited state electron doesn’t The excited state electron doesn’t stay “excited”. It will fall back to the ground state quickly. When the electron returns to the ground state, energy is released in the form of light. One example of this is lasers.

Electrons in Atoms We are most concerned with electrons because electrons are the part of the atom involved in chemical reactions. We are most concerned with electrons because electrons are the part of the atom involved in chemical reactions. Electrons are found outside the nucleus, in a region of space called the electron cloud. Electrons are found outside the nucleus, in a region of space called the electron cloud. Electrons are organized in energy levels of positive integer value (n = 1, 2, 3,...). Electrons are organized in energy levels of positive integer value (n = 1, 2, 3,...). Within each energy level are energy sublevels, designated by a letter: s, p, d, or f. Within each energy level are energy sublevels, designated by a letter: s, p, d, or f. Each sublevel corresponds to a certain electron cloud shape, called an atomic orbital. Each sublevel corresponds to a certain electron cloud shape, called an atomic orbital.

The electron cloud is like an apartment building.

The energy levels are like floors in the apartment building. The energy levels are like floors in the apartment building.

The sublevels are like apartments on a floor of the building. Just like there are different sizes of sublevels, there are different sizes of apartments: 1 bedroom, 2 bedroom, etc. The orbitals are like rooms within an apartment.

The electrons are like people living in the rooms. The electrons are like people living in the rooms.

What do these orbitals look like? The s, p, d and f orbitals look different and increase in complexity (f-orbitals not shown… they are very complex) The s, p, d and f orbitals look different and increase in complexity (f-orbitals not shown… they are very complex)

Number of electrons in each sublevel depends on number of orbitals! Each orbital can hold a maximum of 2 electrons. Each orbital can hold a maximum of 2 electrons. An “s” sublevel contains 1 s orbital. How many total electrons can fit in an s sublevel? An “s” sublevel contains 1 s orbital. How many total electrons can fit in an s sublevel? 2 A “p” sublevel contains 3 p orbitals. How many total electrons can fit in a p sublevel? A “p” sublevel contains 3 p orbitals. How many total electrons can fit in a p sublevel? 6 A “d” sublevel contains 5 d orbitals. How many total electrons can fit in a d sublevel? A “d” sublevel contains 5 d orbitals. How many total electrons can fit in a d sublevel? An “f” sublevel contains 7 f orbitals. How many total electrons can fit in an f sublevel? An “f” sublevel contains 7 f orbitals. How many total electrons can fit in an f sublevel? 14 14

The Aufbau Principle Three rules govern the filling of atomic orbitals. The first is: Three rules govern the filling of atomic orbitals. The first is: The Aufbau Principle: Electrons enter orbitals of lowest energy first. The Aufbau order lists the orbitals from lowest to highest energy: (“Aufbau” is from the German verb aufbauen: to build up) The Aufbau Principle: Electrons enter orbitals of lowest energy first. The Aufbau order lists the orbitals from lowest to highest energy: (“Aufbau” is from the German verb aufbauen: to build up) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 14 6d 10 5p 6 6s 2 4f 14 5d 10 6p 6 7s 2 5f 14 6d 10

The Pauli Exclusion Principle An atomic orbital may hold at most 2 electrons, and they must have opposite spins (called paired spins). An atomic orbital may hold at most 2 electrons, and they must have opposite spins (called paired spins). When we draw electrons to show these opposite spin pairs, we represent them with arrows drawn in opposite directions. When we draw electrons to show these opposite spin pairs, we represent them with arrows drawn in opposite directions. Write this down in your notes if you haven’t!

Hund’s Rule When electrons occupy orbitals of equal energy (such as three p orbitals), one electron enters each orbital until all the orbitals contain one electron with spins parallel (arrows pointing in the same direction). Second electrons then add to each orbital so that their spins are paired (opposite) with the first electron in the orbital. When electrons occupy orbitals of equal energy (such as three p orbitals), one electron enters each orbital until all the orbitals contain one electron with spins parallel (arrows pointing in the same direction). Second electrons then add to each orbital so that their spins are paired (opposite) with the first electron in the orbital. Write this down in your notes if you haven’t!

An electron configuration uses the Aufbau order to show how electrons are distributed within the atomic orbitals. An electron configuration uses the Aufbau order to show how electrons are distributed within the atomic orbitals. How to read a segment of an electron configuration: How to read a segment of an electron configuration: Example 3p 6 3 = energy level p = sublevel 6 = # of electrons Now, let’s look at how to put these together for a specific element!

Electron Configurations This is one way to represent the electrons of an atom. We will try a few together: This is one way to represent the electrons of an atom. We will try a few together: Element Total # of electrons Electron Configuration carbon fluorine magnesium argon s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 2 1s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 5

Orbital Diagrams Orbital diagrams show with arrow notation how the electrons are arranged in atomic orbitals for a given element. Orbital diagrams show with arrow notation how the electrons are arranged in atomic orbitals for a given element. Element Total # of electrons Orbital Diagram carbon fluorine magnesium argon ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ 1s 2s 2p 3s 3p 18 ↑↓ ↑↓ ↑ ↑. 1s 2s 2p ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓. 1s 2s 2p 3s ↑↓ ↑↓ ↑↓ ↑↓ ↑. 1s 2s 2p

Valence electrons Electrons in the outer energy level of an atom. They are like the front lines of an army, because they are the ones involved in chemical reactions (valence electrons get shared or transferred during reactions). Electrons in the outer energy level of an atom. They are like the front lines of an army, because they are the ones involved in chemical reactions (valence electrons get shared or transferred during reactions). The number of valence electrons that an atom has is directly responsible for the atom’s chemical behavior and reactivity. The number of valence electrons that an atom has is directly responsible for the atom’s chemical behavior and reactivity. We can represent the number of valence electrons pictorially by drawing the electrons around the symbol in a “dot diagram”. The electrons are drawn in on each side of the symbol and are not paired up until they need to be. We can represent the number of valence electrons pictorially by drawing the electrons around the symbol in a “dot diagram”. The electrons are drawn in on each side of the symbol and are not paired up until they need to be. Eg.. Be. Eg.. Be.

ElementElectron Configuration# Valence Electrons Electron Dot Structure Li Be B C N O F Ne. B. ̇. Be. Li. 11s 2 2s 1 1s 2 2s 2 1s 2 2s 2 2p 1 1s 2 2s 2 2p 2 1s 2 2s 2 2p 3 1s 2 2s 2 2p 4 1s 2 2s 2 2p 5 1s 2 2s 2 2p C. ̇.. N : ̇. : O : ̇.. : F : ̇.. : Ne : ̇̇ ̇̇

The Periodic Table The rows on the periodic table are called periods The rows on the periodic table are called periods The columns on the periodic table are called groups or families The columns on the periodic table are called groups or families Elements within a group or a family have similar reactivity. What do you know about all elements in a period that could explain this? Elements within a group or a family have similar reactivity. What do you know about all elements in a period that could explain this? They have the same number of valence electrons They have the same number of valence electrons

Since many of the families on the periodic table have such similar properties, they some have specific names that you need to know. Get out your periodic table and label each section as we look at them together. Since many of the families on the periodic table have such similar properties, they some have specific names that you need to know. Get out your periodic table and label each section as we look at them together.

Alkali Metals are group 1 and are the most reactive metals. They form +1 ions by losing their highest energy s 1 electron. 1 valence electron. Alkaline Earth Metals are in group 2. the form 2+ ions by losing both of the electrons in the highest energy s orbital. 2 valence electrons. Halogens are in group 17 and they are the most reactive nonmetals. The form -1 ions by gaining 1 electron to fill the highest energy p orbital. They have 7 valence electrons. Noble Gases are in group 18. They do not form ions because they have a full outer shell of electrons and do not need any more electrons. They do not form compounds.8 valence electrons The transition metals include groups 3 through 12 and these metals all lose electrons to form compounds

Electromagnetic Radiation Electromagnetic radiation is a form of energy that travels through space in a wave-like pattern. eg. Visible light Electromagnetic radiation is a form of energy that travels through space in a wave-like pattern. eg. Visible light It travels in photons, which are tiny particles of energy that travel in a wave like pattern. Although we call them particles, they have no mass. Each photon carries one quantum of energy. It travels in photons, which are tiny particles of energy that travel in a wave like pattern. Although we call them particles, they have no mass. Each photon carries one quantum of energy. These photons of energy travel at the speed of light (c) = 3.00 x 10 8 m/s in a vacuum These photons of energy travel at the speed of light (c) = 3.00 x 10 8 m/s in a vacuum

What is a wave and how do we measure it? Frequency (ν) – number of waves that passes a given point per second (measured in Hz) Frequency (ν) – number of waves that passes a given point per second (measured in Hz) Wavelength (λ) – shortest distance between two equivalent points on a wave (measured in m, cm, nm) Wavelength (λ) – shortest distance between two equivalent points on a wave (measured in m, cm, nm)

Electromagnetic spectrum (EM) The electromagnetic spectrum shows all wavelengths of electromagnetic radiation – the differences in wavelength, energy and frequency differentiates the different types of radiation. The electromagnetic spectrum shows all wavelengths of electromagnetic radiation – the differences in wavelength, energy and frequency differentiates the different types of radiation. Note that as the wavelength increases, the energy and the frequency decrease. Note that as the wavelength increases, the energy and the frequency decrease.

Ground state vs. Excited state Electrons generally exist in the lowest energy state they can. We call this the ground state. Electrons generally exist in the lowest energy state they can. We call this the ground state. However, if energy is applied to the electrons, they can be “excited” to a higher energy and we call this an excited state. However, if energy is applied to the electrons, they can be “excited” to a higher energy and we call this an excited state. The excited state electron doesn’t The excited state electron doesn’t stay “excited”. It will fall back to the ground state quickly. When the electron returns to the ground state, energy is released in the form of light. One example of this is lasers.

Nuclear Forces The force that holds the protons together within the nucleus even though there are repulsive forces that would otherwise push the positive protons away from each other. (also known as strong force) The force that holds the protons together within the nucleus even though there are repulsive forces that would otherwise push the positive protons away from each other. (also known as strong force)

RadiationRadiation Radiation-it’s the transfer of energy Radiation-it’s the transfer of energy Radioactivity-The spontaneous emission of radiation by an unstable nucleus. Radioactivity-The spontaneous emission of radiation by an unstable nucleus.

Good vs. Bad Ionizing Ionizing Has enough energy to kick off an ion. Has enough energy to kick off an ion. Very high energy Very high energy Non ionizing Non ionizing Does not have enough energy to kick off an ion Does not have enough energy to kick off an ion Low energy Low energy

A. Types of Radiation Alpha particle (  ) Alpha particle (  ) helium nucleus helium nucleus paper 2+ Beta particle (  -) Beta particle (  -) electron electron 1- cardboard Positron (  +) Positron (  +) +’ly charged e - +’ly charged e - 1+ Gamma (  ) Gamma (  ) high-energy photon high-energy photon 0 concrete thick lead

B. Nuclear Decay Alpha Emission Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!!

B. Nuclear Decay Beta Emission Beta Emission electron

B. Nuclear Decay Gamma Emission Gamma Emission Usually follows other types of decay. Usually follows other types of decay. Transmutation Transmutation One element becomes another. One element becomes another.

B. Nuclear Decay Why nuclides decay… Why nuclides decay… need stable ratio of neutrons to protons need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

C. Half-life Half-life (t ½ ) Half-life (t ½ ) Time required for half the atoms of a radioactive nuclide to decay. Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. Shorter half-life = less stable.

F ission F ission splitting a nucleus into two or more smaller nuclei splitting a nucleus into two or more smaller nuclei 1 g of 235 U = 3 tons of coal 1 g of 235 U = 3 tons of coal

F ission F ission chain reaction - self-propagating reaction chain reaction - self-propagating reaction critical mass - the minimum critical mass - the minimum amount of fissionable material needed to sustain a chain reaction

Fission Uranium-235 is the only naturally occurring element that undergoes fission. Uranium-235 is the only naturally occurring element that undergoes fission. Uranium - 235

Fission Why does fission produce so much energy? Why does fission produce so much energy? Small quantities of mass are converted into appreciable quantities of energy. Small quantities of mass are converted into appreciable quantities of energy. E = mc 2

Fission 1 gram matter Energ y 700,000 Gallons of high octane gasoline

Fusion combining of two nuclei to form one nucleus of larger mass combining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain thermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 20 tons of coal 1 g of fusion fuel = 20 tons of coal occurs naturally in stars occurs naturally in stars

Fission vs. Fusion 235 U is limited 235 U is limited danger of meltdown danger of meltdown toxic waste toxic waste thermal pollution thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable FISSIONFISSION FUSIONFUSION

Nuclear Power Nuclear Power Fission Reactors Fission Reactors Cooling Tower

Nuclear Power Fission Reactors Fission Reactors

Nuclear Power Fusion Reactors (not yet sustainable) Fusion Reactors (not yet sustainable)

Nuclear Power Fusion Reactors (not yet sustainable) Fusion Reactors (not yet sustainable) Tokamak Fusion Test Reactor Princeton University National Spherical Torus Experiment

Synthetic Elements Transuranium Elements Transuranium Elements elements with atomic #s above 92 elements with atomic #s above 92 synthetically produced in nuclear reactors and accelerators synthetically produced in nuclear reactors and accelerators most decay very rapidly most decay very rapidly