1. Introduction to Atomic Structure

2. Matter – is anything that takes up space and has mass
Mass- is the amount of matter in any object
All matter has observable and measurable properties

3. c. Properties of Matter

4. i. Chemical properties – characteristics that describe how a substance reacts with other substance to produce a different substance.
1. Requires that scientists have a basic understanding of the particles that make up the substance
a. Example: A chemical property of iron is that it will react with oxygen to form rust
b. Example: Helium does not react with any other substance
Helium atom
Formation of Rust

5. ii. Physical properties – are characteristics that can be observed without changing the composition of a substance. Examples:
density (mass / volume)
color
hardness
freezing point
boiling point
ability to conduct current

6. II. Elements – a substance that cannot be broken down into simpler substances by chemical means
Each element has a characteristic set of physical and chemical properties
there are 90 elements that occur naturally on Earth
98% of the earths crust is made up of only 8 elements
Every element is represented by a symbol (1 or 2 letters)
Organized in a table called the “periodic table of the elements”

7. III. Atoms- the smallest unit of an element
a. Structure: even though atoms are tiny, they are made up of even smaller parts
i. Nucleus: Made of protons and neutrons
Protons: Particles with a positive charge
Neutrons: particles with no charge
ii. Electron cloud
Electrons: Particles with a negative charge
Electron cloud: a region of space that surrounds the nucleus

8. iii. Atomic number: the number of protons in an atom
elements are arranged in the periodic chart by order of their atomic number
uncharged atoms have the same number of electrons and protons
Number of Protons? 6 28 4
Number of Protons?
Number of Protons?

9. iv. Atomic mass – the sum of the number of protons and neutrons in an atom
1. because an individual atoms has very little mass, weight is given in atomic mass
a. atomic mass is the mass (weight) of one mole (6.022 x 10²³) of atoms of any elements
# of Protons
# of Neutrons
Carbon 12
Carbon 13
Carbon 14 6 6 6 7 6 8

10. v. isotopes – an atom with the same number of protons, but a different number of neutrons
I. isotopes have slightly different properties than other atoms of the same element

11. IV. Valence electrons
a. It is believed that electrons orbit the nucleus of an atom in several levels called shells
b. the electrons in the outermost level called valence electrons determine the chemical properties of the element

12. C. The periodic table
i. table arranged into columns and rows
ii. columns are called groups
groups are determined by the number of electrons in the outermost shell
elements in the same group can be expected to behave chemically in similar ways
The number of valence electrons increases as you move ACROSS the Periodic Table
Elements in the same group can be expected to behave chemically in a similar way

13. iii. Rows are called periods
The row number tells you how many energy levels, or shells, the element has.
Elements in the period have the same number of rings.
The number of rings increases as you move DOWN the Periodic Table
Each ring has a maximum number of electrons that can fit on it.
Each ring CAN and will hold LESS than the maximum number of electrons. e- e- e-
Ring
Max Number of e- 1 2 3 e- e- e- e- e- 2 e- e- e- e- N e- e- 8 e- e- e- e- e- e- 16 e- e- e- e- e- e-

14. Bohr Models
 a. First, depending on the atom, figure out its number of rings (energy levels)
i. Examples:
Hydrogen is on row #1 of the periodic table so it has energy level
Next, figure out the atom’s total number of electrons
Going in a clockwise direction, fill each energy level with the appropriate number of electrons
Period (row) 1 H H H

15. Bohr Models
 a. First, depending on the atom, figure out its number of rings (energy levels)
i. Examples:
Hydrogen is on row #1 of the periodic table so it has energy level
Lithium is on row #2 of the periodic table so it has 2 energy levels.
Next, figure out the atom’s total number of electrons
Going in a clockwise direction, fill each energy level with the appropriate number of electrons
Period (row) 2 Li Li

16. VI. Lewis Dot Diagrams 
Find the valence electron number of the atom (remember that it equals the column or group number).
Each valance electron is represented by a dot.
Around the atom’s symbol, place the appropriate number of valence electrons
Example: Boron
Lewis Dot Structure B B
Bohr Model