the atom1788

Vocabulary

• ATOM-An atom is the smallest unit that maintains the characteristics of an element– Nucleus- The center of the atom, contains protons

and neutrons– Electron Cloud –Region surrounding the nucleus

containing the electrons

• ELEMENT- A chemical substance that is composed of atoms with the same number of protons in the nucleus

The Atom

The Atom

NucleusProtons

Neutrons

The NucleusProton-A positively charged sub-atomic particle

(+). Atomic Mass=1 amuThe number of protons is the same as the

atomic number

Li3

7 The atomic massThe atomic mass

The Atomic Symbol

The Nucleus

Neutrons –A sub-atomic particle in the nucleus--Has a mass equal to 1 atomic mass unit

--Neutron do not have a charge (0)To calculate the number of neutrons in an element…

Li3

7

The atomic number

The atomic massThe atomic mass

The atomic mass-The atomic number The number of neutrons

The Atom

The Electron Cloud

• Electrons-• The number of electrons equals the number of protons• Sub-atomic particle with a negative charge (-)• Mass of an electron is negligible• Electrons behave as if in a 3-D orbit

• Valence Electrons– The outer most electrons– Valence electrons are responsible for bonding

Periodic Table

• Groups- Arranged by the number of valence electrons

Each group has similar bonding properties• Periods-Arranged by increasing atomic weight

Periods have the same number of shells

Example: Group 1…1 valence electronGroup 2…2 valence electronsGroup 3…3 valence electrons

Example: Period 1…1 valence shellPeriod 2…2 valence shellsPeriod 3…3 valence shells

Periodic Table

Periods go across on the periodic table

Periods have the same number of “shells”

1234567

Periodic TableGroups go down on the periodic table

Elements in the same group, have the same number of valence electrons

1 23 4 5 6 87

Let’s look at a few elements…

Hydrogen 1= Proton 1= electron

Let’s look at a few elements…

Helium 2=protons 2=neutrons2=electrons

Let’s look at a few elements…

Lithium 3=protons 4=neutrons3=electrons

Let’s look at a few elements…

Fluorine9=protons 10=neutrons

9=electrons

Let’s look at a few elements…

Argon18=protons 22=neutrons

18=electrons