Chapter 17 cp
Atoms
4.2/4.3 The Structure of the Atom & Modern Atomic Theory
JOURNAL:
1.
2.
3.
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.
Studying Atoms
ANCIENT GREEKSDEMOCRITUS:
 “atomos” = indivisible, uncut
 Different types of atoms with specific properties
ARISTOTLE:


Only 4 elements
No limit to divisions
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.
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
Thomson’s “plum pudding” Atomic Model
Explained neutral
atoms with charges
Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms
positive charge is concentrated in the nucleus
Thomson’s “plum pudding”
Atomic Model
Studying Atoms
RUTHERFORD’S ATOMIC THEORY: all atoms
positive charge is concentrated in the nucleus
Discovered:

Uranium emits fast moving positive particles
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!!
Studying Atoms – Gold Foil Experiment
4.1 The Gold Foil Experiment
RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus
Studying Atoms – Modern Atomic Theory
Bohr Atom:
Electrons
are in energy levels
Electrons move when they gain or lose energy
(example)
Parts of an ATOM:
Subatomic particles – distinguished by mass,
charge and location
Subatomic particle PROPERTIES
 Protons (p+):
In the nucleus
 Charge of 1+
 Mass of 1
 DEFINES THE ELEMENT
(equals the ATOMIC NUMBER)

Protons (p+):

Atoms of DIFFERENT elements have
DIFFERENT numbers of protons
Subatomic particle PROPERTIES
 Neutrons (n°):




In the nucleus
NO charge
Mass of 1
Protons + neutrons = the ATOMIC MASS
Neutrons (n°):

Atoms of the same element with
DIFFERENT numbers of neutrons are called
ISOTOPES

Neutrons (n°):

ISOTOPES of Hydrogen. Same Atomic #,
different Mass #
Electrons (e-):





In ENERGY LEVELS around the nucleus
Charge of 1Mass 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.
Electrons (e-):

Change ENERGY LEVELS when the atom GAINS or
LOSES energy
The most stable
electron arrangement
Electrons (e-):

CurrentTheory – “Electron Cloud Model” (p116-17)

Orbitals that show most PROBABLE location of electrons
Electrons (e-):

Atoms of the same element with different
number of ELECTRONS are called IONS
IONS: form to make the outermost shell stable
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
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)
Al = 13
Ti = 22
Sn = 50
Os = 76
Er = 68
How many protons does each atom have?
 The number of protons are equal to the atomic number.
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
11
Carbon
6
6
6+6
12
Oxygen
8
8
8+8
16
Sodium
11
12
11+12
23
Copper
29
34
29+34
63
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

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
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

Neutral Atoms

In the nucleus, which particles have
charge?


What charge do they have?


Protons
Positive
What particle is opposite that charge?

Electrons
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.
Practice
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
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.
REVIEW
1.
Draw a Bohr Atom Model of Hydrogen, Carbon,
and Oxygen on the back of your worksheet.
2.
Which subatomic particles belong in the nucleus?
3.
Which subatomic particles belong on the rings?
4.
What is the difference between ‘ground state’ and
‘excited state’ of an atom?