Download Ionic and Covalent bonding (WLC)

Chapters 7 & 8
Ionic Bonding and Ionic Compounds
Covalent Bonding
Valence Electrons
• Valence Electrons are the electrons of an atom which
are in the highest energy level.(outermost levels)
• They largely determine the chemical properties of an
element.
• The # of Valence electrons in an atom is directly
related to the elements grouping on the periodic table
(1a,2a,etc…)
• Valence electrons are usually the only electrons used
in chemical bonds and for the most part only the
valence electrons are used in atomic dot structures.
Electron Dot Structures
• Electron dot structures are diagrams that
show valance electrons as dots
• The inner electrons and the atomic nuclei
are included in the letter symbol for the
element being represented.
Example of Oxygen
Electron Dot Structure
Electron Dot Structure
• Electron Dot Structure-a notation that
depicts valence electrons as dots around the
atomic symbol of the element; represents
inner electrons of the nucleus
Xe has 8 valence electrons
Pb has 4 valence electrons
Cations and Anions
• A cation is a positively charged ion. It is caused by
an atoms loss of a valance electron.
• The most common cations are caused by the loss
of an electron from metal atoms which, having 1-3
valance electrons, can easily lose one or two.
• An anion is an atom with a negative charge, they
are created by the gain of an electron to a neutral
atom.
Cations/Anions
• Cation-positive charged ion produced from loss of
valance electron from an atom
• Example: NaNa+ + e• Anion-atom or group of atoms with negative
charge
• Example: Cl + e-Cl• Octet Rule-electrons try to gain the configuration
of a noble gas, which has 8 valence electrons
Cation and Anion Formulas
• Cation Example Formula
• Na 1s22s22p63s1Na+ 1s22s22p6
Octet: 2s22p6
• Anion Example Formula
• Cl 1s22s22p63s23p5Cl- 1s22s22p63s23p6
Octet: 3s23p6
• Halide Ions-the ions produced when halogens gain electrons
Ionic Bonds
• Because Anions and Cations have opposite
charges, naturally, they would attract each
other. They do so by using electrostatic
forces. Forming Ionic Bonds
• At room temperature most ionic
compounds are crystalline solids, these
structures are very stable.
Argonite (CaCo3)
Ionic Compounds
Ionic Bonds
Ionic Compounds
• Ionic Compounds-a
compound composed of positive
and negative ions
• Properties of Ionic Compounds:
» crystalline solid @ room
temperature
» Ions arranged in repeating
3D patterns
» Very stable
» High melting temperature
Metallic Bonds
• Metals are made up of closely packed
cations rather than neutral atoms
• These cations are surrounded by mobile
valence electrons which can drift freely
from one metal to another
• Metallic bonds consist of the attraction of
free floating valence electrons for the
positively charged metal ions
Metals and Free Electrons
Metal Properties
• Metals are good conductors of electricity because these
'free' electrons carry the charge of an electric current when a
potential difference (voltage!) is applied across a piece of metal.
Metals are also good conductors of heat. This is also due to
the free moving electrons. Non-metallic solids conduct heat
energy by hotter more strongly vibrating atoms, knocking
against cooler less strongly vibrating atoms to pass the particle
kinetic energy on. In metals, as well as this effect, the 'hot' high
kinetic energy electrons move around freely to transfer the
particle kinetic energy more efficiently to 'cooler' atoms.
• Unlike ionic solids, metals are very malleable, they can be
readily bent, pressed or hammered into shape. The layers of
atoms can slide over each other without fracturing the structure
(see below). The reason for this is the mobility of the
electrons. When planes of metal atoms are 'bent' or slide the
electrons can run in between the atoms and maintain a strong
bonding situation. This can't happen in ionic solids.
Properties of Metals
• Metals are good conductors of electrical
currents because electrons can flow freely
• They are ductile and malleable because
electrons can move freely.
• An alloy is a mixture composed of two or
more elements, at least one of which is
metal
Alloys
• Alloys-mixtures composed
of two or more elements
at least one of which is a
metal
• Alloys are prepared by melting
the mixture of the ingredients
and then cooling the mixture
• Brass is an alloy of copper and
zinc
• Bronze is an alloy of 7 parts
copper and one part tin
• Steel is an alloy of iron and
carbon. It is corrosion resistant
ductile, hard and tough.
Alloy Properties
• Shows an alloy mixture. It is NOT a compound but a
physical mixing of a metal plus at least one other
material (shown by red circle, it can be another metal
eg Ni, a non-metal eg C or a compound of carbon or
manganese, and it can be bigger or smaller than iron
atoms). Many alloys are produced to give a stronger
metal. The presence of the other atoms (smaller or
bigger) disrupts the symmetry of the layers and
reduces the 'slip ability' of one layer next to another.
The result is a stronger harder less malleable metal.
Alloy Properties
Covalent Bonds and Polarity
• Covalent bonds involve electron sharing
between atoms
• Groups forming covalent bonds: non-metals
( and Hydrogen)…all want to gain, “tug-ofwar” on electrons
• These bonds share electrons, causing each
side to possibly have a different charge
• Non- polar covalent is when the bonding
electrons are shared equally(no charge)
• polar covalent bond is when the electrons
Electrostatic Charge Applications
• Car shocks http://www.stopshox.com/
• Getting “shocked” http://www.staticsol.com/articles/static_shocks.htm
• air purifiers
• http://www.oreck.com/airpurifiers/air8.cfm?keycode=CK690#five_st
age
Double Bonds
Bond Types
• Non-Polar- no charges, both sides have
equal pulls; diatomic, ex. O2
• Polar-partial charges, one side has a greater
pull than the other; ex. H2O
• Ionic- full charges; transfer of electrons
Crystalline shape, ex. NaCl
Non-Polar: Equal Sharing
Polar Compounds
Polar Compound
Hydrogen Bonding