Bonding

Ionic and covalent

Key Terms1

Chemical formula– the combination of chemical symbols and subscripts to indicate what the elements are in the compound and how many atoms of each element are in the compound Example: H2O= two hydrogen atoms and 1

oxygen atom.

Key Terms2

The octet rule– each atom wants to have 8 electron in its outer most energy level. Atoms can share, take, or give away

electrons to accomplish this. Valence electrons– electrons in the outer

most energy level that are responsible for the reactivity of that atom.

Key Terms3

Lewis structure (electron-dot notation)– valence electrons are shown as dots around the element’s symbol. Label the # of Ve- on your periodic table. Only used for main block elements Because each orbital can hold two electrons,

electrons are grouped in pairs forming the shape of a box around the element’s symbol.

Paired electrons can also be represented by a dash instead of dots if they are being shared in a compound.

Key terms4

Ions Ion– any atom that has given up or taken

electrons to create a positive or negative charge.

This is done to fill the highest energy level. Cations (cat-ion) – any element that has given

away its electrons to become a positively charged ion. Cations are metals.

Anions– any element that has taken electrons to become a negatively charged ion. Anions are nonmetals.

Atoms and charges What happens when an atom gains or looses

an electron? The atom becomes charged!

Example: Copper has an atomic number of 29.This means copper has 29 electrons(-) and

29 protons(+). If copper were to loose two electrons, what would copper’s charge be?

29 Protons (+)+ 27 Electrons (-) 2 Protons left over, each proton has a positive

charge so the charge of copper would be +2!

Practice Problem

Oxygen has an atomic number of 8 and an atomic mass of 16. How many neutrons does oxygen have?

Answer: 16= N+8, N=8 What would Oxygen’s charge be if it

gained two electrons? Answer: 8(+ protons) + 10 (- electrons)=-

2

Ionic Bonding

Ionic Bonding Ionic bonding– any bond between metals

and nonmetals (cations and anions) Charges are based on how many Ve- are

needed to fill the outer shell or drop to the previous full shell. Label this on your table.

The charges must cancel each other out. Example: Na (+1) and Cl (-1)=NaCl (0) Example: Ca (+2) and F (-1)=CaF2 (0)

Ionic compounds are usually solids and in a crystal structure (crystal lattice).

Ionic Compounds Both ions should have complete outer shells

after bonding. Both elements should have noble gas

electron configurations When naming, the first element always

stays the same, but the last element should end with –ide Ex. MgO= Magnesium Oxide instead of

Magnesium Oxygen Ex. CaCl2= Calcium Chloride vs Chlorine

Covalent Bond Key Terms1

Molecule: a group of atoms held together by covalent bonds

Covalent bond: when atoms share electrons Nonpolar covalent bond: electrons are

equally shared by all atoms and the electrical charge is balanced

Polar covalent bond: electrons are not shared equally and there is an imbalance in the electrical charge surrounding the molecule.

Polar vs. nonpolar Polar nonpolar

Key Terms2

Polar bonds: when atoms in a molecule have an uneven electron distribution.

Bond length: average distance between two bonded atoms

Bond energy: energy required to break a chemical bond and form neutral isolated atoms.

When the bond length gets shorter, the bond energy gets higher

Key Terms3

Lewis structures must be used to create covalent compounds (molecules). Sorry no short cuts this time.

Single bond: when only two electrons are being shared between two atoms

Double bond: when 4 electrons are being shared between two atoms

Triple bond: when 6 electrons are being shared between two atoms

Covalent Bonds

Covalent Bonding2

There are no ions involved with covalent bonds which means no charges.

This is a bond between two nonmetals.

Electrons are shared. The magic number is still 8.

Covalent properties

covalent bonds can produce solids, liquids, or gaseous molecules

they are poor conductors of electricity They have low melting points and boiling

points They are usually very dull in appearance

Covalent Nomenclature

When naming covalent compounds, you MUST use prefixes for the first and second words

The only exception is if you only have one atom for the first element.

the less electronegative (furthest to the left on the p/t) element is given first and its full element name is written

-ide is still needed at the end of the second element as well as a prefix

Covalent molecule prefixes

1. Mono-2. Di-3. Tri-4. Tetra-5. Penta-6. Hexa-7. Hepta-8. Octa-9. Nona-10. Deca-

Covalent nomenclature

Examples Dihydrogen monoxide (H2O)

Sulfur trioxide (SO3)*there is only one sulfur so no prefix is needed.

Trisilicon tetranitride (Si3N4)

Dinitrogen Pentaoxide (N2O5)