Chemical formulae Flashcards
What is the formula of an element?
The formula of any element is its symbol. The exception to this are the diatomic elements. They exist as pairs of atoms joined together.
What is a molecule?
A molecule is a group of two or more atoms, which are joined together by covalent bonds.
What are the seven diatomic molecules?
Fluorine Chlorine Oxygen Hydrogen Nitrogen Bromine Iodine
What is a compound?
A compound is made up of two or more elements chemically combined.
How is the chemical formula of a two-element compound worked out?
The chemical formula is worked out by using the valency of the atoms involved in the bond.
What is valency?
The valency is the number of electrons an atom can lose or gain to have a full shell of electrons, Elements in the same group have the same valency.
what are the valencies for the groups 1-7
1-1 2-2 3-3 4-4 5-3 6-2 7-1
What are the rules for writing chemical formula for a compound?
- Identity and find the symbol(s) for the element(s) in the periodic table.
- Write the valency at the top right-hand corner of each symbol
- Use the cross over method( swap and drop)
- write down the formula(simplest whole-number ratio of atoms)
What happens if the valency of each element is the same?
If the valency of each element is the same then there is only one of each in the formula. The valencies cancel.
What number do we not write in a formula?
Do not write the number ‘1’ in the formula.
How do you find the group ions?
The group ions can be found on page 8 of the data booklet.
Which group has its own valency?
Compounds with two or more elements ending in -ite and -ate contain groups of atoms. The group has its own valency which is equal to the size of the charge.
What is the valency of the transition metals?
The valency of the transition metal is a roman numeral which is inserted into the name of the compound immediately after the name of the transition metal.
What number is this roman numeral (I)?
One
What number is this roman numeral (II)?
Two
What number is this roman numeral (III)?
Three
What number is this roman numeral (IV)?
Four
What number is this roman numeral (V)?
Five
What is this roman numeral (VI)?
Six
What elements are the exception for the valencies of transition metals and have only one valency?
Zinc-2
Silver-1
How do you write the formulae for a compound with a prefix?
If a compound has a prefix the valency rules do not apply.
What number is the prefix mono?
One.
What number is the prefix di?
Two.
What number is the prefix tri?
Three
What number is the prefix tetra?
Four.
What is the prefix penta?
Five.
What is the prefix hexa?
Six.
What are ionic compounds made up from?
Ionic compounds are made up of ions. (Usually a metal ion and a non-metal ion). The ionic formula of a compound includes the charges of the ions.
Do metals form positive or negative ions?
Metal form positive ions.
Do non metals form positive or negative ions?
Non metals form negative ions.
What is the valency of an ionic formulae?
The valency is the charge on the ion.
Can the charge of an ion change?
The charge of an ion will never change.
How do you workout the charge when writing ionic formula for an element?
For an element the charge is its valency then add + for metal ions and - for non metal ions.
