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Atoms, Ions, and the Periodic Table

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Presentation on theme: "Atoms, Ions, and the Periodic Table"— Presentation transcript:

1 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?

2 Democritus ( BC)

3 Democritus ( BC) 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 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!

4 John Dalton ( )

5 John Dalton ( ) All matter is composed of extremely small particles called atoms. All atoms of one element are identical. 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 are indivisible. In addition, they cannot be created or destroyed, just rearranged.

6 Dalton’s theory has two flaws:
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: 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.

7 Discovery of the Electron JJ Thomson (1856-1940)

8 Discovery of the Electron JJ Thomson (1856-1940)
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 positive cage. Diagram of plum pudding model:

9 Discovery of the Nucleus Ernest Rutherford (1871-1937)

10 Discovery of the Nucleus Ernest Rutherford (1871-1937)
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.

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

12 Questions about Rutherford’s experiment:
I. If gold atoms were solid spheres stacked together with no space between them, what would you expect would happen to particles shot at them. Explain your reasoning. The He nucleus would have been deflected straight back because it would have a much larger, heavier particle. 2. What does Ernest Rutherford’s experiment suggest about the structure of the atom; in other words, how can Rutherford’s evidence be used to correct the plum pudding model? Draw a diagram.   It shows there must be a dense area of great mass in the atom  3. Can you explain why Rutherford concluded that the mass of the gold nucleus must be much greater than the mass of an alpha particle (helium nucleus)?    The He nucleus was deflected or reflected and couldn’t move the nucleus 4. Do you think that, in Rutherford's experiment, the electrons in the gold atoms would deflect the alpha particles significantly? Why or why not? No, because the He nucleus has a much greater mass than an electron. 5. Rutherford experimented with many kinds of metal foil as the target. The results were always similar. Why was it important to do this? To ensure that this property was not specific to gold and that a generalization could be made for all atoms. Rutherford then discovered the proton, and next, working with a colleague, James Chadwick ( ), he discovered the neutron as well.

13 Models of the Atom - Niehls Bohr

14 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. Diagram of Bohr model:

15 Quantum Mechanical Model

16 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.

17 Sub-Atomic Particles Each atom contains different numbers of each of the three SUBatomic particles
Symbol Charge Molar Mass Where found Proton p+ +1 Nucleus Neutron n0 Electron e- -1 Electron Cloud “A neutron walked into a bar and asked how much for a drink. The bartender replied, “For you, no charge.”

18 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 electrons in one atom of that element (with an ion, the electrons will be different) **Therefore, protons = electrons in a neutral atom**

19 Atomic Mass mass of an element measured in amu (atomic mass units)
Averages of all known isotopes are listed on the periodic table Mass # = # of p+ + # of n0 So: Mass # = Atomic number + # of n0

20 Isotopes Isotopes are atoms of an element with the same number of protons but different numbers of neutrons. Change in # of n0 = Change in the Mass # 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 Another way is :

21 protons are WHITE BEANS electrons are POPCORN KERNNELS
neutrons are RED BEANS atomic # = # of protons in an atom mass # = # of protons + # of neutrons + BAG # of p e n Atomic # Mass # Element Name w/ mass # (isotope notation) example 4 3 7 Lithium - 7 3 3

22 Determining Average Atomic Mass
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. Formula: (Mass1 * Abundance1) + (Mass2 * Abundance2) + (Mass3 * Abundance3) + etc….

23 Example of Average atomic mass calculation
Given: 12C = 98.89% at 12 amu 13C = 1.11% at amu Calculation: (98.89%*12 amu) + (1.11%* amu) = (0.9889*12 amu) + (0.011* amu) = 12.01 amu

24 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? The answer is: ( * amu) + ( * amu) + ( * amu) = amu Now compare this mass for Neon to the mass on the periodic table!

25 Electrons in Atoms Electrons are found outside the nucleus, in a region of space called the electron cloud. We are most concerned with electrons because electrons are the part of the atom involved in chemical reactions.

26 Electrons are organized first by energy levels of positive integer value (n = 1, 2, 3,...).
The energy levels are like floors in an apartment building…

27 Within each energy level are energy sublevels, designated by a letter: s, p, d, or f.
The sublevels are like types of apartments on a floor of the building. Just like there are different sizes of sublevels, there are different sizes of apartments: 1 bedrooms (s orbital) 3 bedrooms (p orbitals) 5 bedrooms (d orbitals) 7 bedrooms (f orbitals)

28 S p The orbitals are like rooms within an apartment. d f

29 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)


31 Number of electrons in each sublevel depends on number of orbitals!
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? 2 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? 10 An “f” sublevel contains 7 f orbitals. How many total electrons can fit in an f sublevel? 14

32 The electrons are like people living in the rooms.

33 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: Example p6 3 = energy level p = sublevel 6 = # of electrons Now, let’s look at how to put these together for a specific element!

34 The Aufbau Principle 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) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10

35 What does that mean? The Energy levels will fill from lowest energy level to highest So tenants will have to fill the apartments on the ground floor first. When we write the electron configuration, the first, large number represents the Energy Level (Floor of the apartment building)

36 The Pauli Exclusion Principle
An atomic orbital may hold at most 2 electrons, and they must have opposite spins (called paired spins). What does this mean? When we draw electrons to show these opposite spin pairs, we represent them with arrows drawn in opposite directions. ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ 1s 2s p s p

37 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.

38 What does this mean? When writing Orbital Diagrams, you place one up arrow in every orbital before adding a down arrow. ↑↓ ↑↓ ↑ ↑ ↑. 1s s p ↑↓ ↑↓ ↑↓ ↑ ↑ . 1s s p In the apartment analogy, each person gets their own bedroom before people start doubling up in rooms.

39 Electron Configurations
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 6 1s2 2s2 2p2 9 1s2 2s2 2p5 1s2 2s2 2p6 3s2 12 1s2 2s2 2p6 3s2 3p6 18

40 Orbital Diagrams 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 s p 6 ↑↓ ↑↓ ↑↓ ↑↓ ↑ . 1s s p 9 ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓. 1s s p s 12 18 ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ 1s 2s p s p

41 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). 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. Eg. . Be .

42 Electron Configuration Electron Dot Structure
Element Electron Configuration # Valence Electrons Electron Dot Structure Li Be B C N O F Ne 1s2 2s1 1 Li. 1s2 2s2 2 . Be . 1s2 2s2 2p1 3 . B . ̇ . . C . ̇ 1s2 2s2 2p2 4 . . N : ̇ 5 1s2 2s2 2p3 . : O : ̇ 1s2 2s2 2p4 6 .. : F : ̇ 7 1s2 2s2 2p5 .. : Ne : ̇̇ ̇̇ 1s2 2s2 2p2 8

43 s p 1 2 d 3 f 4

44 Electromagnetic Radiation
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. These photons of energy travel at the speed of light (c) = 3.00 x 108 m/s in a vacuum

45 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) Wavelength (λ) – shortest distance between two equivalent points on a wave (measured in m, cm, nm)

46 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. Note that as the wavelength increases, the energy and the frequency decrease.

47 Ground state vs. Excited 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. 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.


49 The Periodic Table The rows on the periodic table are called periods
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? They have the same number of valence electrons

50 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.

51 Alkali Metals are group 1 and are the most reactive metals
Alkali Metals are group 1 and are the most reactive metals. They form +1 ions by losing their highest energy s1 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. The transition metals include groups 3 through 12 and these metals all lose electrons to form compounds 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

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