1. Unit 2: Chemical Reactions and Radioactivity 4
Unit 2: Chemical Reactions and Radioactivity 4.1 Atomic Theory & Bonding

2. History of Atomic Theory
Around 500 BC, Greek philosophers originated the thought that all matter is composed of atoms.
The word atom comes from the Greek word atomos, which means “indivisible.”
Around 1800: John Dalton revived discussion about the atom
1898: J.J. Thomson discovered the electron
Soon after: Ernest Rutherford discovered the structure of the atom
Niels Bohr: proposed the concept of electron shells, created the “Bohr Model”

3. Atoms have a neutral charge Fun Fact:
What is an Atom?
smallest particle of an element that still has the properties of that element
An atom = proton(s) + electron(s) + neutron(s) (PEN)
Atoms have a neutral charge
Fun Fact:
50 million atoms, lined up end-to-end = 1 cm

4. Structure of an Atom: The nucleus is at the centre of an atom
composed of protons (positive charge) and neutrons (neutral charge)
Electrons (negative charge) exist in the space surrounding the nucleus

5. area surrounding the nucleus
Subatomic Particles:
Atoms are made up of smaller particles known as sub-atomic particles.
Name
Symbol
Charge
Location
Atomic Mass
Proton p 1+
nucleus
1 AMU
Neutron n
Electron e 1–
area surrounding the nucleus
1/1836 (0)

6. Draw an atom!
Label the nucleus, protons, neutrons, electrons, and indicate the charge on each of them.

7. Subatomic Particles Found in the nucleus only
Protons – positive charge (+)
Neutrons – neutral charge (0)
Found around the nucleus
Electrons – negative charge (-)

8. An ELEMENT is made up of one type of atom
The element, oxygen, is O
IONS are atoms with a charge.
The ion of oxygen is O2-
Atom vs Ion Drawing on Board

9. COMPOUNDS are made up of several (2 or more) elements
Atoms can join together to form MOLECULES. The oxygen molecules are O2 (groups of atoms)
COMPOUNDS are made up of several (2 or more) elements
Hydrogen and oxygen are elements
H2O is a compound

10. Numbers to Remember : # protons = identity of element
# of protons = # of electrons in every atom
AND ONLY IN ATOMS!!! (not ions!!!!)
Nuclear charge = charge on the nucleus = # of protons
Atomic number = # of protons
= identity of element
= # of electrons in atoms (not ions!)
# Electrons in an atom = atomic number (also # protons)
Mass number = # of protons + # of neutrons

11. Ion Charge
(when the atom is changed to an ion by gaining or losing electrons)
Atomic Number
Element Name
Element Symbol
Average Atomic Mass

12. Ion Charge
(when the atom is changed to an ion by gaining or losing electrons)
Atomic Number
Element Name
Element Symbol
Average Atomic Mass

13. Periodic Table Writing Activity

14. Families of the Periodic Table:
Columns of elements are called groups, or families
All elements in a family have…
similar properties
bond with other elements in similar ways
have the same number of valence electrons
Family names (on the periodic table!):
Group 1 = alkali metals
Group 2 = alkaline earth metals
Group 17 = the halogens
Group 18 = noble gases
Periods are horizontal rows on the periodic table

15. Where are the following?
INCREASING REACTIVITY
Where are the following?
Atomic Number
Period
Group/Family
Metals
Non-metals
Transition metals
Metalloids
Alkali metals
Alkaline earth metals
Halogens
Noble gases

16. Periodic Table & Ion Formation:
Atoms gain and lose electrons to form ions to become more stable (full valence shell)
Metals lose electrons & become positive ions (cations)
Some metals can have more than one charge (multivalent)
ie. Iron, Fe, loses either 2 (Fe2+) or 3 (Fe3+) electrons
Non-metals gain electrons & become negative ions (anions)
Atoms do this in an attempt to have the same number of valence electrons as the nearest noble gas – to become stable