1. Chapter 17 - cp
Atoms

2. 4.2/4.3 The Structure of the Atom & Modern Atomic Theory
JOURNAL:
QUIETLY work on the Atomic Math worksheet FIRST
Then, work on the“Not So Bohr-ing Atoms” Worksheet from the back table.
Use the Periodic Table I gave you to help you.

3. Studying Atoms ANCIENT GREEKS- DEMOCRITUS:
“atomos” = indivisible, uncut
Different types of atoms with specific properties
ARISTOTLE:
Only 4 elements
No limit to divisions

4. Studying Atoms
DALTON’S ATOMIC THEORY: all matter is made of particles that cannot be divided
Evidence:
Compounds have fixed compositions
H2O
Chemical reactions are a rearrangement of solid atoms.

5. Studying Atoms
THOMSON’S ATOMIC THEORY: all matter is made of particles that CAN be divided
EVIDENCE:
Particles collected on metal plate
The particles ALWAYS had a mass 1/2000 of a Hydrogen atom.
The beam was always attracted to the positive side

6. Thomson’s “plum pudding” Atomic Model
Explained neutral atoms with charges

7. Thomson’s “plum pudding” Atomic Model
Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus
Thomson’s “plum pudding” Atomic Model

8. Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus
Discovered:
Uranium emits fast moving positive particles

9. SHOULD GO STRAIGHT THROUGH!!
Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus
If you shoot these positive particles at other atoms (Thomson’s plum pudding atom), what would happen to the particle?
SHOULD GO STRAIGHT THROUGH!!

10. Studying Atoms – Gold Foil Experiment

11. 4.1 The Gold Foil Experiment
RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus

12. Studying Atoms – Modern Atomic Theory
Bohr Atom:
Electrons are in energy levels
Electrons move when they gain or lose energy
(example)

13. Subatomic particles – distinguished by mass, charge and location
Parts of an ATOM:
Subatomic particles – distinguished by mass, charge and location

14. Subatomic particle PROPERTIES Protons (p+):
In the nucleus
Charge of 1+
Mass of 1
DEFINES THE ELEMENT
(equals the ATOMIC NUMBER)

15. Protons (p+):
Atoms of DIFFERENT elements have DIFFERENT numbers of protons

16. Subatomic particle PROPERTIES Neutrons (n°):
In the nucleus
NO charge
Mass of 1
Protons + neutrons = the ATOMIC MASS

17. ISOTOPES Neutrons (n°):
Atoms of the same element with DIFFERENT numbers of neutrons are called
ISOTOPES

18. Neutrons (n°):
ISOTOPES of Hydrogen. Same Atomic #, different Mass #

19. Electrons (e-): In ENERGY LEVELS around the nucleus Charge of 1-
Mass of 1/1836 of a p+
Equal to the number of protons
The outermost shell of electrons is called the VALENCE SHELL which holds the VALENCE ELECTRONS.
Take out Bohr Diagram Sheet.

20. The most stable electron arrangement
Electrons (e-):
Change ENERGY LEVELS when the atom GAINS or LOSES energy
The most stable electron arrangement

21. Electrons (e-): CurrentTheory – “Electron Cloud Model” (p116-17)
Orbitals that show most PROBABLE location of electrons

22. Electrons (e-):
Atoms of the same element with different number of ELECTRONS are called IONS

23. IONS: form to make the outermost shell stable

24. 4.2/4.3 The Structure of the Atom & Modern Atomic Theory
OCTET RULE:
Take out a lined sheet of paper, draw a circle for a nucleus and then three rings around the nucleus.
2 electrons in 1st shell
Protons and neutrons in nucleus
8 electrons in 2nd shell
8 electrons in 3rd shell

25. Atomic Number Practice
Use your periodic table to find the atomic number of the following elements:
Aluminum (Al)
Titanium (Ti)
Tin (Sn)
Osmium (Os)
Erbium (Er)
How many protons does each atom have?
The number of protons are equal to the atomic number.
Al = 13
Ti = 22
Sn = 50
Os = 76
Er = 68

26. Mass Number
The mass number of an atom is the sum of the number of protons and neutrons in the nucleus.
Element
Protons
Neutrons
Mass Number
Boron 5 6
5+6
Carbon
6+6
Oxygen 8
8+8
Sodium 11 12
11+12
Copper 29 34
29+34 11 12 16 23 63

27. Practice
Determine the number of protons and neutrons in the following atoms:
Lithium – Atomic Number = 3
Mass Number = 7
Argon – Atomic Number = 18
Mass Number = 39
Strontium – Atomic Number = 38
Mass Number = 88

28. Atomic Number & Mass Number
If you know the atomic number and mass number, you can determine the number of neutrons. Mass Number - Atomic Number Number of Neutrons

29. Answers
Determine the number of protons and neutrons in the following atoms:
Lithium – Protons = 3
Neutrons = 7 – 3 = 4
Argon – Protons = 18
Neutrons = 39 – 18 = 21
Strontium – Protons = 38
Neutrons = 88 – 38 = 50

30. Neutral Atoms In the nucleus, which particles have charge?
Protons
What charge do they have?
Positive
What particle is opposite that charge?
Electrons

31. (+3) + (-3) = 0, so the atom is neutral.
Neutral Atoms
In the atom:
The number of protons equals the number of electrons.
Li has 3 protons, so has a charge of +3.
Li also has 3 electrons that add up to -3.
ADDED TOGTHER, the overall charge is:
(+3) + (-3) = 0, so the atom is neutral.

32. Practice Magnesium, Protons = 12 Beryllium, Protons = 4
Determine how many electrons the following atoms have:
Magnesium, Protons = 12
Beryllium, Protons = 4
Nitrogen, Atomic Number = 7
Bromine, Atomic Number = 35
12 Electrons
4 Electrons
7 Electrons
35 Electrons

33. Bohr Models of the Atoms
Each atom has shells in which the electrons can fit.
1st Shell: fills to 2 electrons
2nd Shell: fills to 8 electrons
3rd Shell: fills to 18 electrons
4th Shell: fills to 32 electrons
Start filling the smallest/closest shell first.

34. REVIEW
Draw a Bohr Atom Model of Hydrogen, Carbon, and Oxygen on the back of your worksheet.
Which subatomic particles belong in the nucleus?
Which subatomic particles belong on the rings?
What is the difference between ‘ground state’ and ‘excited state’ of an atom?