Chemical Bonding

Science Investigations

What is a chemical bond?

Electrical attraction between the nucleus of one atom and the valence electrons of another

An element’s properties are due to its valence electrons

What diagram shows the valence electrons of an atom?

Octet Rule

Atoms will gain/lose electrons through bonding to have 8 valence electrons to be stable like a noble gas

Exceptions: Helium and Hydrogen only need two valence electrons

Electronegativity

Definition: the attraction of an atom for electrons

Highest for nonmetals

Most electronegative atom is F (Fluorine) and has a value of 4.0

Noble gases do not have a value because they are stable and don’t need electrons

Electronegativity

Scale (write on periodic table), tells you the type of bond between atoms

0-0.3 = non-polar covalent

>0.3-1.7 = polar covalent

>1.7- 4.0 = ionic

Ionic Bonds

A metal atom (positive charge) gives electrons to a nonmetal atom (negative charge)

Electronegativity difference: >1.7-4.0

Rule of thumb:

A metal (alkali or alkaline earth) + nonmetal = ionic

A transition metal + nonmetal = ionic or covalent

Examples: LiF, CaO

Covalent Bonds

Atoms share electrons

Two types:

Polar Covalent: Unequal sharing of electrons

Nonpolar Covalent: Equal sharing of electrons

Covalent Bonds

Rule of thumb:

Two nonmetal atoms that are different = polar covalent

Ex.: CO2, H2O

Two nonmetal atoms that are the same = nonpolar covalent

Ex.: H2

Electronegativity Difference: >0.3-1.7 (polar covalent), 0-0.3 (nonpolar covalent)

Polar vs. Nonpolar

Polar: dissolves in water

Nonpolar: do not dissolve in water

Metallic Bonds

Bond between 2 metal atoms

Electrons are shared equally between all metal atoms and are free to move from atom to atom (sea of electrons)

This makes metals good conductors of heat and electricity