advanced chemistry t4 y10

ions

• atoms that gain or lose electrons

• if atoms lose electrons, they become positively charged cations

• if atoms gain electrons they beocme negatively charged anions

• atoms are unstable, valence shells are incomplete

• atoms will lose or gain electrons to get a complete outer shell

ionic compounds

• cations and anions can ionically bond together to form ionic compounds that are neutrally charged

• e.g. magnesioum forms a 2+ ions (Mg 2+) - loses 2 valence electrons

• chlorine forms a 1- ion ( Cl -) - gains 1 valence electron

• so we need 2 chlorine ions to balance out the charge of the one magnesium ion, this forms a neutral compund

multivalent metal compounds

• many metals are multivalent meaning the metals form two or more different oistive ions with different charges

covalent compounds

• two non-metals covalently bond

• covalent bonding involves the sharing of electrons to achieve electron stability

diatomic molecules

• 7 elements that exist naturally as diatomic molecules

• they covalently bond with themselves to achieve stability,

• when they are seen in word eqaution know that they will be diatomic

• hydorgen, nitrogen, fluroine, oxygen, iodine, chlorine, bromine

mole

• Avagadro’s number is 6.02 × 10²³

• 1 mole = 6.02 × 10²³ atoms or molecules

• no. of moles = number of particles. number or particles per mol

• n= no. particles/ 6.02 × 10²³

Molar Mass

• number of grams per mole for a substance

• it is equal to the relative atomic mass for an element, and the sum of elemental masses for a compund

• gmol ^-1

• number of moles (n)= mass(g)/ molar mass ( gmol ^-1)

• n=m/M

steps for stoichiometry

1. mass of a given substance, calculate moles

2. moles of a given substance

3. use balenced chemical equation

4. moles required of substance

5. calculate mass

percentage yield

• theoretical yield is found in calculation

• actual/ experimental is the actual amount - mass that is given in equation

• %yield = actual yield/theoretical yield x 100

effective nuclear charge

• the attractive positive charge of nuclear protons acting or felt by valence electrons

• it is always less than the total number of protons

• effective nuclear charge = number of protons in the nucleus - number of total inner shell electrons

• it is the number of valence electrons

across a period

• the energy level (or shell) remains the same

• the number of protons in the nucleus increases and therefore so does its positive charge

• the effective nuclear charge increases

down a group

• the effective nuclear charge stays the same

• the number of electron shells increases

• the valence electrons are further from the nucleus

electronegativity

• it is a result of effective nuclear charge

• electronegativity is the ability of the nucleus of an atom to attract electrons

• when a bond is formed the two atoms in the bond are in a ‘tug of war’ for electrons

• the atom with the greater electronegativity “ wins” or pulls the valence electrons closer to its nucleus

ionic bonds , electro negativity

• between a metal and a non-metal

• one atom loses it’s electron to another atom

• electro negativity difference is greater than 1.8

covalent bonds, electro negativity

• between two non metals

• electrons are shared

• if the electronegativity difference is less than 0.4 - valence lectrons are shared equally between two atoms than its is a pure/non-polar covalent

• if the electronegativity id between 0.4 and 0.8 than the valence electrons are still shared but sit closer to the nucleus of the atom with the larger electronegativity - polar covalent