GSCI 163

Lecture 5

Review

• Electrons in an atom are distributed in shells, orbitals and energy levels.

• When electrons absorb photons they jump to higher orbitals

• They move back up by emitting a photon whose energy correspond to the change in energy level

Activity

• Finding the emission lines of different compounds.

Chemistry

• Electrons in an atom are distributed in shells, orbitals and energy levels.

• The way electrons are shared will determine how elements combine with each other to form compounds.

• The highest or last shell of an atom is the valence shell

• The valence shell determines the chemistry and properties

The periodic table

Various groups

• Metals and non-metals– Metals tend to lose

electrons in chemical reactions

– Non-metals tend to gain (or share) electrons in chemical reactions

Semi-metals have both metallic and non-metallic properties

– Most reactive metal Cesium– Most reactive non-metal Fluorine

Noble gases

• The valence shell is full. Thus they almost never react.

– Argon gas (Ar) is used as an inert gas in light bulbs to prevent the filament, made of tungsten (W), from reacting under intense heat

Other families• Alkali metals

– Only one valence electron; very soft metals– React so easily with Oxygen (O) and moisture that they need to be stored under oil

• Alkaline earth metals– Two valence electrons; harder than alkali metals– Not so reactive.

• Halogens– Seven electrons in the valence shell– Very active non-metals

• Fluorine – highly corrosive, • Chlorine – purifying agent, • Bromine – desinfectant

• Semi-metals (semi-conductors)– 3,4 or 5 electrons in the valence shell– Makes them behave both as metals and insulators

Atomic size

• Increase when:– Add a new shell

(moving down a group) since electrons are farther away from the nucleus

– Number of protons decrease (across a period) since electrons are more loosely bound by electrostatic force

Cs ~ 0.47 nm He ~ 0.064 nm

Ionization energy

• Energy required to remove one electron from the outer shell

H

He

Hardest elements to remove one electron from

Octet rule

• Most common elements have electrons on the s and p orbitals of their outmost shells

• We can fit 2 electrons on s and 6 on p, with a total of 8 electrons

Octet rule: atoms will combine with other atoms in such a way that gives a full shell of 8 electrons

Naming compounds

• We represent compounds with a chemical formula:

H2O

• Names are also used to identify the compound unambiguously

Symbol of the element

Number of atoms of the element

Compounds with special names

There are no rules for these. Their names are learned individually

Metal and a non-metal

• Groups 1A, 2A plus Aluminum (Al), Zinc (Zn) and Silver (Ag). They form only one ion.

• Rule for binary compounds:– Name of the metal + non-metal with ending –ide

Examples:NaCl – Sodium ChlorideAl2O3 –

Ca3N2 –

Two non-metals

• Rule: – The less metallic element (farther left and/or farther down the

periodic table) comes first. The second is named with ending –ide .– For more than one element use Greek prefixes: di(2), tri(3),

tetra(4), penta (5), hexa (6), hepta (7), octa (8).

Examples:HCl – hydrogen chlorideCS2 –

PBr3 –

IF7 –

Compounds with polyatomic ions

• Metal plus a polyatomic ion:Rule: name of the metal + the name of

of the polyatomic ion

Example:ZnSO4 – Zinc Sulfate

NaC2H3O2 –

Mg(NO3)2 –

K3PO4 –

Next class

Calculating reactions

• To prepare for the class read:– Handout pages 17 to 20 (day 5)– Presentation by Rebecca Cross, Acids and Bases

• To prepare for the quiz read:– Handout pages 16 (day 4)– Power point for this class– Your class notes