1.2: Atoms, moles and the mole concept Flashcards
What is an atom?
- smallest unit of an element
- contains a nucleus with neutrons and protons, surrounded by orbiting electrons
- An atom has no overall charge
What is an element?
- A substance that can’t be broken down into anything simpler by chemical means
- An element contains only one type of atom
What is a molecule?
Two or more atoms covalently bonded together
What is a compound?
Two or more elements chemically joined together
What is an ion?
An atom or group of atoms that have lost or gained one or more electrons and as a result, carry a positive or negative charge
What is a chemical equation?
A chemical equation represents a chemical reaction using the formulae of the substances involved. These substances can be elements, compounds and ions.
What is a diatomic molecule?
contains 2 atoms covalently bonded together
What are the diatomic molecules you need to recall?
- hydrogen
- nitrogen
- oxygen
- fluorine
- chlorine
- bromine
- iodine
- astatine (At)
what is the formulae of ozone?
O₃
What are the two other elements that have multiple atoms in their molecules?
phosphorus - P₄
Sulfur - S₈
Usually written as just P or S
What is the difference with noble gases?
They have 8 electrons in the outer shell which makes them extremely stable.
This means that they are unreactive
What is the octet rule?
The tendency of elements to acquire a noble gas electron configuration
What ions does the octet rule not apply to?
iron (II) Fe ²+
Cobalt (III) Co³+
Copper (I) Cu+
Manganese (IV) Mn⁴+
What is the ionic half-equation of magnesium?
Mg –> Mg²+ + 2e-
Ionic half equations and metals
Metals lose one or more electron, so electrons are put on the right-hand side
Ionic half equations and non-metals
Non-metals gain one or more electrons, electrons are put on the left-hand side of the equation
What are polyatomic ions?
Contain atoms of more than one element bonded together.
What are covalent compounds?
Usually made up from two or more non-metal elements
What are Ionic compounds?
Usually contain ions of both metal and non-metal elements (exception - ammonium)
What does -ate mean when added to an element (e.g. sulfate)
Oxygen is present
What does -ite mean when added to an element
oxygen present but LESS than ate
What does ‘ium’ mean for ions
Positive ions are formed
What is the Ar?
Ar is the average value calculated from the actual masses of isotopes of elements and their relative abundances.
How do you calculate Relative atomic mass?
(mass of isotope x %) + (mass of an isotope x %) / 100
what is the formula both relative molecular mass and relative formula mass represented by?
Mr
How do you calculate Mr?
adding the relative atomic masses found on the periodic table
How do you calculate the % by mass of an element?
Total mass of all the atoms of a particular element / Mr of the substance x 100
What is a mole?
The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12.
What is Avagadro constant?
One mole of substance contains 6.02 x 10²³ particles of that substance
What is the molar mass?
The mass of one mole of any substance is the same as its Ar or Mr in grams - measured in gmol-1
What are moles used for?
To determine how much product will be made or how much reactant will be needed to complete a reaction
How do you calculate moles from mass?
Moles = mass / Mr (or Ar)
n = m/mr
How do you calculate the % yield?
% yield = actual moles (mass) / theoretical moles (mass) x 100
what is the molar volume?
1 mole of any gas will occupy 24dm³ (24000cm³) at room temp
BECAUSE one mole of any gas contains the same number of particles
How do you calculate the volume of gas from moles?
Volume (dm³) = mol x 24dm³³ OR
volume (cm³) = mol x 24000
How do you calculate moles from volume of gas?
Moles = volume in (dm³) / 24dm³
OR
Moles = volume in (dm³) / 24000
How do you calculate the concentration of a solution?
Conc = moles / vol in dm³
OR
moles = conc x vol in dm³
OR
volume in dm³ = n/c
What can concentration also be measured in?
gdm-³
How do you change from cm³ to dm³
divide by 1000
What can a titration be used for?
To determine the concentration of an acid or base. Titrating known with unknown substance
What specialist equipment is used in titrations?
Top pan balance
burette
volumetric flask
bulb pipette
tap
conical flask
How do you calculate the percentage error overall?
sum of individual percentage errors for each piece of equipment used
% error = uncertainty of apparatus x number of readings / quantity measured x100
acid + alkali –>
salt + water
What is the empirical formula?
the simplest number ration of the atoms of each element present in a compound
What is the molecular formula?
The actual number of atoms of each elements present in a molecule
what is the charge on the elements in the periodic table groups - 1,2,3,5,6,7
1: +1
2: +2
3: +3
5: -3
6: -2
7: -1
