Elements and the Periodic Table

Periodic Table: A structured arrangement of elements that helps us to explain and predict physical and chemical properties.

Chemical Families and Compounds

Covalent (molecular) compounds: form when two nonmetals combine.

Carbon dioxide CO2

Ionic compounds: form when a metal and a non-metal combine

Sodium chloride NaCl

Groups and Families

The vertical columns in the periodic table are called groups or families.

Group 1 – Alkali Metals

Ø  Shiny

Ø  Tend to combine with group 17 elements to form white solids that are very soluble.

Group 2 – Alkaline Earth Metals

Ø  Shiny

Ø  Often combine with group 16 elements to form white solids that are very insoluble.

Group 17 – Halogens

Ø  Nonmetallic

Ø  Usually gases

Ø  Very reactive

Group 18 – Noble Gases

Ø  Nonmetallic

Ø  Gases

Ø  Very unreactive and do not form compounds (they do not combine with other elements)

Atomic Structure

Atoms consist of:

1. A nucleus made of positively charged protons and non-charged neutrons. The number of protons is always equal to the atomic number. The number of neutrons plus protons is equal to the mass number.

2. A group of organized negatively charged electrons. In a neutral atom the number of electrons is the same as the atomic number.

Electrons are organized into compartments or orbitals called “shells”.

Bohr-Rutherford Diagrams

Electrons are arranged around the nucleus in groups or orbitals containing 2 and then 8 electrons.

Neon has 10 electrons.

Chemical Bonding

Ionic (metal and nonmetal)

Ø  How can a sodium atom get rid of its extra electron to become chemically stable?

Ø  Where can a fluorine atom get the extra electron it needs to make a stable octet?

à Stable Octet is the very stable (unreactive)

NOBLE GAS Group.

Metal Non-metal

Na +1 F-1

- Need to loose an electron - Need to gain an electron

to become stable, and at to become stable in its

the same time loose an 2nd energy level.

energy level (outer shell).

- It looses a valence electron

Ø  Groups 1, 2, and 3 will loose electrons

To become

Ø  Groups 6 and 7 will gain electrons “Stable Octet”

Ionic charge: numerical value of the electric charge with a plus or minus sign (the +1 for Na after it combines with F)

Covalent (molecular bonds)

Non metals can also share electrons so that each atom has access to 8 electrons in their outermost orbital.

We can use the number of electrons needed to be lost or gained to predict the number of atoms involved in the formation of a molecule.