3 1 formulae and relative masses

The seven elements that exist as diatomic molecules are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine.

False. The molecular formula of water is H2O.

The subscript number in a molecular formula represents the number of atoms of that element in the molecule.

A simple molecule is a molecule made up of a small number of atoms.

The molecular formula of ethene is C2H4.

False. Diatomic molecules contain two atoms of the same element.

A molecular formula shows the type and number of atoms in a molecule.

A chemical symbol is a one or two-letter abbreviation used to represent an element in chemical formulas and equations.

The dot and cross diagram represents ammonia, NH3, which consists of one nitrogen atom and three hydrogen atoms.

The displayed formula represents methane, CH4, which consists of one carbon atom and four hydrogen atoms.

Empirical formula is the simplest whole number ratio of the atoms or ions present in a compound.

The empirical formula of propene is CH2.

False. Organic molecules often have different empirical and molecular formulae.

The formula of an ionic compound is always an empirical formula.

The molecular formula is a multiple of the empirical formula. It indicates the exact numbers of each atom in the compound.

False. Empirical formula shows the simplest whole number ratio of atoms in a molecule.

The formula of the ionic compound formed from Fe2+ and Cl- is FeCl2.

The formula of the ionic compound formed from Li+ and Cl- is LiCl.

The empiticval formula of the ionic compound is AgF.

The formula of the ionic compound formed from Na+ and CO32- is Na2CO3.

True. A balanced chemical equation has the same number of atoms of each element on both sides, in accordance with the Law of Conservation of Mass.

The word equation for the reaction of silicon with oxygen to form silicon dioxide is: silicon + oxygen silicon dioxide

2Br- + Cl2 Br2 + 2Cl- is an ionic equation.

A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction.

The missing numbers to balance the equation are: 2H2O2 2H2O + O2

Products are the new substances which are on the right-hand side of the arrow in a chemical equation, formed by the reaction of reactants.

The constituent ions are:

The symbol equation for the reaction of magnesium with chlorine to form magnesium chloride is: Mg + Cl2 MgCl2

False. The balanced symbol equation for the reaction of sodium with chlorine is:
2Na + Cl2 2NaCl

The missing numbers to balance the equation are: N2 + 3H2 ⇌ 2NH3

Spectator ions are ions which appear on both sides of an ionic equation and are eliminated from the final equation.

2KI + Br2 2KBr + I2 is not an ionic equation because there are no ions.

The relative atomic mass, Ar, as the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of carbon-12.

The relative atomic mass of an element is found on the Periodic Table.

False. The relative atomic mass of fluorine is 19. The atomic number / number of protons in fluorine is 9.

Mr is the symbol for the relative formula mass and it refers to the total mass of the substance, which is the sum of the relative atomic masses of all atoms in a molecule.

To calculate the relative formula mass of a substance, you have to add up the relative atomic masses of all the atoms present in the formula.

False. Relative molecular mass does not apply to ionic compounds.

Molar mass refers to the mass of one mole of a substance.

The relative formula mass of CuCO3 is: 63.5 + 12 + (16 x 3) = 123.5

The relative molecular mass of C5H5N is: (12 x 5) + (1 x 5) + 14 = 79

The difference between relative molecular mass and relative formula mass is that relative moleculas mass only applies to covalent compounds. Relative formula mass applies to all compounds.

The relative molecular mass of NH4NO3 is: 14 + (1 x 4) + 14 + (16 x 3) = 80

True. The relative formula mass of CaCO3 is = 40+12 +(16 x 3) = 100