unit 1 revision chapter 2 - 8. chapter 2 – a particle view of matter what you should be able to...

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Chapter 2 - 8

Chapter 2 – A particle view of matterWhat you should be able

to do:• Describe the structure of

the atom in terms of the arrangement of protons, neutrons and electrons

• Isotopes– Calculate abundance and

Relative Atomic Mass• Electron configuration

– Excited and ground state

Atomic Theory

• Explains the structure of atoms• Atoms are made up from sub-atomic particles.• Protons – found in the nucleus and have a positive

charge. Relative mass of 1• Neutrons – found in the nucleus and have no charge.

Relative mass of 1• Electrons – orbit the nucleus in specific energy levels

known as shells – take up most of the space occupied by an atom. Relative mass of 0.0005

Structure of the atomProtons:-Found in nucleusPositive charge (+ve)Mass = 1Number of protons is known as the Atomic number.Each element has a different number of protons.Protons are made form quarks and gluons.

Neutrons:-Found in nucleusNo chargeMass = 1Neutrons act to stabilise the nucleus and hold the protons together with the strong force.The Relative atomic mass is the number of protons + number of neutrons.Neutrons are made form quarks and gluons.

Electrons:-Found in (orbits) shells around the nucleus.Each shell and sub-shell represent a particular energy level that the electrons are found at. These energy levels can be explained by quantum mechanics.The number of electrons equals the number of protons unless the atom forms an ion.

Isotopes

Mass Spectrometer

• Most elements form isotopes

• An Isotope is an element that has atoms that

have a different number of neutrons.

• The RAM on the periodic table is an average for

that element taking into account the abundance of

the isotopes for that element.

• Isotope calculations are an important part of

chemistry. Page 38 of your text gives you the

formula and an example of these types of

calculations.

• A mass spectrometer can be used to detect the

presence and number of isotopes present in a

sample of an element.

Mass spectrum of Bromine molecules

Shells and Sub Shells

Chapter 3 – The periodic tableWhat you should be

able to do:• Explain the periodic

variation of elements

• Locate an element on the periodic table given electron configuration

Chapter 4 – Relative Atomic Mass and the Mole

What you should be able to do:

• Calculate Relative Atomic Mass from isotopes and mass spectrometers

• n=m/M• N=n x NA

• Calculate % by mass• Determine empirical

formula• Determine molecular

mass

Mole calculationsn = m M

Number of mol = mass of chemical in grams divided by its Molar Mass.

m = n x M Mass of a chemical in grams = number of mol x Molar mass.

M = m n

Molar Mass of unknown chemical = mass in grams ÷ number of mole

Particles = n x NA Particles present = number of mole x Avogadro's number.

n = Particles NA

Number of mole = Particles present ÷ Avogadro’s Number.

Percentage composition

• Percentage composition tells us the amount by mass of each element present in a compound.

Molar mass = (39.1 x 2) + (52 x 2) + (16 x 7) = 294.2 gmol-1

% Oxygen = (16 x 7) x 100 294.2 1 = 38%

Empirical formula• The simplest whole number ratio of atoms

present in a compound.• H2O C2H3O4 C6H12O6

• You must be able to perform calculations to determine empirical formula.

http://upload.wikimedia.org/wikipedia/commons/thumb/a/ac/Green_tick.svg/600px-Green_tick.svg.png

http://upload.wikimedia.org/wikipedia/commons/thumb/a/ac/Green_tick.svg/600px-Green_tick.svg.png

Molecular formula• The molecular formula is the actual formula of a

chemical which is not always in its simplest form (empirical formula)

To calculate the Molecular Formula:Molecular formula mass / empirical formula mass =

the number of times the empirical formula

Practice Exam Questions

Which of the following atoms is in its ground state?

A.1s22s23s2

B.1s22s22p5

C.1s22s22p63s24s1

D.1s22s22p63s23p63d54s2


The element that can be found in group 2 period 4 of the Periodic Table is:

A.MgB.CaC.SrD.Ba


The percentage by mass of uranium in uranium oxide (U3O8) is:

A.84.8%B.82.3%C.80.1%D.88.5%


The mass of 0.25 mol of aluminium oxide (Al2O3) is:

A.20.45gB.25.23gC.25.50gD.22.19g


The empirical formula of the compound with the composition: 42.9% carbon and 57.1% oxygen is:

A.CO2

B.C2O2

C.COD.C2O


Which of the following atoms has the greatest number of neutrons?

A.57CoB.58FeC.56MnD.56Ni

Practice Exam QuestionsIsotopes are A.Atoms that have the same atomic number but

different numbers of electrons.B.Atoms that have different numbers of protons but

have the same mass number.C.Atoms that have both the same number of protons

and neutrons.D.Atoms that have the same number of protons but

different mass numbers.


Which of the following is not an empirical formula?

A.C2H6

B.CH3COOH

C.H2SO4

D.KCl


The number of atoms present in 0.625 mol of H2O molecules is:

A.6.25 x 1021 B.6.25 x 1022

C.6.25 x 1023

D.6.25 x 1024


The ground state electronic configuration, in terms of subshells, for the chloride ion is:

A.1s22s22p63s23p6

B.1s22s22p63s23p5

C.1s22s22p63s23p63d1

D.1s22s22p63s23p53d1

Practice Exam QuestionsThe electronegativity values of elements in the periodic table have been

found to follow certain trends. The correct statement concerning electronegativity values is that they:

A. Increase from left to right across the periodic table and increase as you go down the table.

B. Increase from left to right across the periodic table and decrease as you go down the table.

C. Decrease from left to right across the periodic table and decrease as you go down the table.

D.Decrease from left to right across the periodic table and increase as you go down the table.


The ground state electronic configuration, in terms of shells, for the chloride ion is,

A.2, 8, 8.B.2, 8, 7.C.2, 8, 6.D.2, 8, 7, 1.

unit 1 revision chapter 2 - 8. chapter 2 – a particle view of matter what you should be able to...

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