2.1.1 atomic structure and isotopes, 2.1.2 compounds, formulae and equations

what was stated in Dalton's atomic theory?

• atoms are tiny particles made of elements

• atoms cannot be divided

• all atoms in an element are the same

• atoms of one element are different to those of other elements

what did Thompson discover about electrons?

• they have a negative charge

• they can be deflected by magnet and electric field

• they have very small mass

explain the plum pudding model

atoms are made up of negative electrons moving around in a sea of positive charge

what were Rutherford's proposals after the gold leaf experiment?

• most of the mass and positive charge of the atom are in the nucleus

• electrons orbit the nucleus

• most of atom's volume is the space between the nucleus and the electrons

• overall positive and negative charges must balance

explain the current model of the atom

• protons and neutrons are found in the nucleus

• electrons orbit in shells

• nucleus is tiny compared to the total volume of the atom

• most of atom's mass is in the nucleus and the electron

what is ther charges of sub-atomic particles?

proton = +1

electron = -1

neutron = 0

what particle has the same mass as a proton?

neutron

which 2 particles make up most of the atom's mass?

protons and neutrons

what letter is used to represent the atomic number of an atom?

Z

what does the atomic number tell us about an element?

atomic number = number of protons in atom

which letter represents mass number?

A

how is mass number calculated?

mass number = number of protons + number of neutrons

how would we calculate number of neutrons?

number of neutrons = mass number - atomic number

define isotope

atoms of the same element with different numbers of neutrons

why do different isotopes of the same element react in the same way?

• neutrons have no impact on the chemical reactivity

• reactions involve electrons, isotopes have the same number of electrons in the same arrangement

what are ions?

charged particles formed when an atom loses or gain electrons

what is the charge of the ion when electrons are gained?

negative

what is the unit used to measure atomic mass

unified atomic mass unit, u

define relative atomic mass

the weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon-12

what is the unit of relative atomic mass

no units

define relative isotopic mass

the mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12

relative atomic mass is the same as which number?

mass number

what 2 assumptions are made when calculating mass number?

1. contributuion of the electron is neglected

2. mass of both proton and neutron is taken as 1.0 u

how to calculate relative molecular mass and relative formula mass?

both can be calculated by adding the relative atomic masses of each of the the atoms making up the molecule or the formula

what are the uses of mass spectrometry?

• identify unknown compounds

• find relative sbundance of each isotope of an element

• determine structural information

how does a mass spectrometer work?

• the sample is made into positive ions

• they pass through the apparatus and are separated according to mass to charge ratio

• a computer analyses the data and produces mass spectrum

how is the group number related to the number of electrons?

group number = number of electrons in outer shell

is the group number indicated by the horizontal row or verticle column in the periodic table

verticle column

do metals usually gain of lose electrons?

lose electrons to form positive ions

which 4 elements don't tend to form ions and why?

• beryllium

• boron

• carbon

• silicon

  it requires a lot of energy to transfer outer shell electrons

what are molecular ions?

covalently bonded atoms that lose or gain electrons

what's the charge of an ammonium ion?

+1

NH₄⁺

what is the charge of a hydroxide ion?

-1

OH⁻

what is the charge of a nitrate ion?

-1

NO₃⁻

what is the charge of a carbonate ion?

-2

CO₃²⁻

hat is the charge of a sulfate ion?

-2

SO₄²⁻

what is emperical formula?

simplest whole number ratio of atoms of each element present in a compound

how to calculate emperical formula?

• divide the amount of each element by its molar mass

• divide the answers by the smallest value obtained

• if there is a decimal, divide by a suitable number to make it into a whole number