2.3 Formulae and Equations
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When atoms lose of gain electrons, they achieve the same electron structure as…
…the nearest noble gas
What do metal atoms on the left of the periodic table form?
Lose electrons to form cations
What do non-metals on the right of the periodic table form?
Gain electrons to form anions
Which elements can form several ions with different charges?
Some metals, mostly transition metals
How can you tell what the ionic charge of some metals are?
The roman numerals correspond Eg. Iron (II) -> Fe2+
What is a binary compound?
Contains only 2 elements
How to name a binary compound:
Use the name of the first element but change the ending of the second elements name to -ide For ionic compounds, the metal ion always comes first
Common polyatomic ions
Ammonium (NH4 +) Hydroxide (OH -) Carbonate (CO3 2-) Sulfate (SO4 2-) Phosphate (PO4 3-)
What does an ionic compound contain
A cation and an anion
How can you work out the formula of an ionic compound
Look at the charges of each ion The overall charge should be zero so the ionic charges must balance Sum of positive charges = sum of negative charges
How to write the formula of an ionic compound
The number of each ion present is shown as a subscript after the ion The ionic charges are usually omitted in the completed formula Brackets are used if there is more than one polyatomic ion
What is a diatomic molecule
Two atoms bonded together Eg. H2, N2, O2, F2, Cl2, Br2 and I2
What are the state symbols
g - gas l - liquid s - solid aq - dissolved in water
How to balance equations
MUST NOT change any chemical formula Balancing numbers go IN FRONT of the chemical formulae and ON THE LINE The equation is balanced when there are the same number of atoms of each element on each side
Can you use fractions when balancing equations
Yes