Physical Science Chapter 4 Atomic Structure

4.1 Studying Atoms Democritus and Aristotle Democritus thought all matter consisted of extremely tiny particles that could not be divided called atoms different types of atoms: in liquids were round and smooth; in solids rough and prickly Aristotle thought there was no limit to the number of times matter could be divided. All substances were built from only 4 elements: Earth, air, fire, & water

Dalton’s Atomic Theory Developed a theory to explain why the elements in a compound always behave in the same way. Main Points 1) All elements are composed of atoms. 2) All atoms of the same element have the same mass, and atoms of different elements have different masses. 3) Compounds contain atoms of more than one element. 4) In a compound, atoms of different elements always combine in the same way. (same ratio)

Thomson’s Model Cathode Rays and Electrons Experiments in the late 1800s by Thompson, showed that cathode rays were composed of negatively charged particles. These particles were named electrons Also developed the plum pudding model of the atom

Thomson’s Cathode-Ray Tube Experiment Chapter 3 Thomson’s Cathode-Ray Tube Experiment Click below to watch the Visual Concept. Visual Concept

Discovery of the Atomic Nucleus Ernest Rutherford The results of their gold foil experiment led to the discovery of a very densely packed bundle of matter with a positive electric charge because some of the alpha particles bounced back Rutherford called this positive bundle of matter the nucleus.

Rutherford’s Gold Foil Experiment Chapter 3 Rutherford’s Gold Foil Experiment Click below to watch the Visual Concept. Visual Concept

“Structure of the Atom” Chapter 4 Lesson 2 “Structure of the Atom”

Subatomic Particles A. An atom 1. smallest part of matter B. Areas of an atom 1. Nucleus – center of an atom -holds protons and neutrons a. Protons (P) – positively charged particle found in the nucleus. -has a mass of 1 -has a charge of 1+ b. Neutrons (N) – non-charged particle found in the nucleus. -has no charge “0”

2. Electron Cloud – area around the nucleus which contains electrons a 2. Electron Cloud – area around the nucleus which contains electrons a. Electrons (e) – negatively charged particle found outside of the nucleus -has a mass of 0 -has a charge of 1- -moves around the outside of the nucleus (like a bee trying to escape a closed jar)

Protons Electrons Neutrons

Particles in an Atom Review Mass Charge Location of particle Proton 1 1+ nucleus Neutron 1 nucleus Electron 1- Electron cloud

Atomic Number Atoms of different elements have different numbers of protons. Atoms of the same element all have the same number of protons. The atomic number of an element is the number of protons of each atom of that element. *Protons dictate the type of element we have* *Electrons always equal the # of protons (this makes the charge of an atom neutral)*

Mass Number always a whole number NOT on the Periodic Table! mass # = protons + neutrons Publishing Company, Inc. always a whole number NOT on the Periodic Table! Average atomic mass is on the table

Isotopes Mass # Atomic # Atoms of the same element with different mass numbers. B/C they differ in # of neutrons Nuclear symbol: Mass # Atomic # Hyphen notation: carbon-12

4. How many neutrons do the following isotopes have 4. How many neutrons do the following isotopes have? Oxygen-14 Titanium-50 Magnesium-22 Potassium-43 Aluminum-23 Iodine-130 6 28 10 24 10 77

Average Atomic Mass Weighted average of all isotopes of one element combined. 1. Found on periodic table underneath chemical symbol. 2. Ex: Carbon = 12.011 Carbon has 3 known isotopes. Carbon-12, 13, and 14. Carbon-12 makes up 99% of all carbon on earth. Carbon-13 and 14 make up 1%.

“Modern Atomic Theory” Chemistry Timeline…pg. 114-115 Chapter 4 Lesson 3 “Modern Atomic Theory” Chemistry Timeline…pg. 114-115

Bohr Model p+ no e- Niels Bohr Energy levels Bohr used data from atomic spectra to propose a planetary model of the atom in which electrons orbit the nucleus, like planets around the sun

Bohr’s Model / Energy Levels 18 electrons 2 electrons e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- 32 electrons e- e- 8 electrons e- e- e- e- e- e- e- e- e- e- nucleus e- e- e- e- e-

Bohr Model of the Atom Click below to watch the Visual Concept.

Energy Levels Possible energies that electrons in an atom can have An electron in an atom can move from one energy level to another when the atom gains or loses energy No 2 elements have the same set of energy levels

Electron Configuration excited state- Electrons move to higher energy level (exists for short time unstable) Light is released is when electrons drops back down to lower energy Color varies based on atom and amount of energy released ENERGY IN PHOTON OUT Absorb photon Emits Photon ground state- lowest energy state of electrons (stable)

Electrons in Energy Levels Number of Orbitals Maximum # of Electrons 1 4 9 16 2 1 8 2 3 18 4 32

Electron Cloud Model Orbital- region of space around the nucleus where an electron is likely to be found (each orbital can hold up to 2 electrons) Electron Cloud is a good approximation of how electrons behave and possible locations in their orbitals (like blades on an airplane)

In Class Assignment 1. Draw a picture of the following atoms with the correct number of e’s, p’s, and n’s… a. Na d. He b. Al e. C c. K f. S