1.1.2 Atomic Structure • Describe protons, neutrons and electrons. • Describe the distribution of mass and charge in an atom. • Describe the contribution of protons and neutrons to the nucleus in terms of atomic number and mass number. • Explain the term isotopes. • Deduce the atomic structure in atoms and ions.

THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are ... Mass / kg Charge / C Relative mass Relative charge PROTON NEUTRON ELECTRON

1 +1 1 -1 1 1836 THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are ... Mass / kg Charge / C Relative mass Relative charge PROTON NEUTRON ELECTRON 1 +1 1.672 x 10-27 1.602 x 10-19 1 1.675 x 10-27 1 1836 -1 9.109 x 10-31 1.602 x 10-19

1 +1 1 -1 1 1836 THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are ... Mass / kg Charge / C Relative mass Relative charge PROTON NEUTRON ELECTRON 1 +1 1.672 x 10-27 1.602 x 10-19 1 1.675 x 10-27 1 1836 -1 9.109 x 10-31 1.602 x 10-19 Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons

1 +1 1 -1 1 1836 THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are ... Mass / kg Charge / C Relative mass Relative charge PROTON NEUTRON ELECTRON 1 +1 1.672 x 10-27 1.602 x 10-19 1 1.675 x 10-27 1 1836 -1 9.109 x 10-31 1.602 x 10-19 Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons 6 x 1.672 x 10-27 + 6 x 1.675 x 10-27 + 6 x 9.109 x 10-31 =

1 +1 1 -1 1 1836 THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are ... Mass / kg Charge / C Relative mass Relative charge PROTON NEUTRON ELECTRON 1 +1 1.672 x 10-27 1.602 x 10-19 1 1.675 x 10-27 1 1836 -1 9.109 x 10-31 1.602 x 10-19 Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons 6 x 1.672 x 10-27 + 6 x 1.675 x 10-27 + 6 x 9.109 x 10-31 = 2.0089 x 10-26 kg

MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus

MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS Na 23 11 Atomic Number (Z) PROTONS

Na 23 11 MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS Na 23 11 THESE ALWAYS GO TOGETHER – ANYTHING WITH 11 PROTONS MUST BE SODIUM Atomic Number (Z) PROTONS

MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS Na 23 11 Atomic Number (Z) PROTONS

MASS NUMBER AND ATOMIC NUMBER THERE WILL BE 12 NEUTRONS IN THE NUCLEUS Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS THERE WILL BE 12 NEUTRONS IN THE NUCLEUS 23 – 11 = 12 Na 23 11 Atomic Number (Z) PROTONS

MASS NUMBER AND ATOMIC NUMBER Atomic Number (Z) Number of protons in the nucleus of an atom Mass Number (A) Sum of the protons and neutrons in the nucleus Mass Number (A) PROTONS + NEUTRONS Na 23 11 Atomic Number (Z) PROTONS

MASS NUMBER AND ATOMIC NUMBER Protons Neutrons Electrons Charge Atomic Number Mass Number Symbol A 19 21 B 20 40 C + 11 23 D 6 E 92 235 F 13 G 16 2- H 27Al3+

MASS NUMBER AND ATOMIC NUMBER Protons Neutrons Electrons Charge Atomic Number Mass Number Symbol A 19 21 40 40K B 20 40Ca C 11 12 10 + 23 23Na+ D 6 12C E 92 143 235 235U F 7 13 13C G 16 18 2- 32 32S2- H 14 3+ 27 27Al3+

Subatomic particles in ions In reduction and oxidation reactions, electrons are transferred. When elements react to form ions, electrons are either lost or gained. This results in a stable electron arrangement. What changes to electrons occur during the formation of positive ions? What changes to electrons occur during the formation of negative ions?

Name Symbol Protons neutrons electrons Hydrogen - 1 H Hydrogen - 2 Hydrogen - 3 Lithium - 6 Lithium - 7 Chlorine - 35 Chlorine - 37 Copper – 63 Copper – 65 Zirconium – 90 Zirconium - 94 1 2 1 Worksheet – isotope table

atom - ion symbol protons neutrons electrons charge hydrogen H hydrogen ion + 1 sodium Na sodium ion magnesium magnesium ion + 2 aluminum aluminum ion + 3 nitrogen nitride ion - 3 oxygen oxide - 2 fluorine fluoride -1 Worksheet – Atoms & ions

The arrangement of the electrons The electrons are found at considerable distances from the nucleus in a series of levels called energy levels. Each energy level can only hold a certain number of electrons. The first level (nearest the nucleus) will only hold 2 electrons, the second holds 8, and the third also seems to be full when it has 8 electrons. These levels can be thought of as getting progressively further from the nucleus. Electrons will always go into the lowest possible energy level (nearest the nucleus) - provided there is space.

What is the electronic arrangement in chlorine ? The Periodic Table gives you the atomic number of 17. Therefore there are 17 protons and 17 electrons. The arrangement of the electrons will be 2, 8, 7 (i.e. 2 in the first level, 8 in the second, and 7 in the third). The electronic arrangements of the first 20 elements

Two important generalisations If you look at the patterns in this table: The number of electrons in the outer level is the same as the group number. (Except with helium which has only 2 electrons. T he noble gases are also usually called group 0 - not group 8.) This pattern extends throughout the Periodic Table for the main groups (i.e. not including the transition elements). So if you know that barium is in group 2, it has 2 electrons in its outer level; iodine (group 7) has 7 electrons in its outer level; lead (group 4) has 4 electrons in its outer level. Noble gases have full outer levels.

23Na+ 19F- 35Cl- 37Cl- 40Ca2+ 39K+ 32S2- 16O2- 14N3- 24Mg2+ 7Li+ Name Symbol Number of protons Number of neutrons Number of electrons Electron configuration 23Na+ 19F- 35Cl- 37Cl- 40Ca2+ 39K+ 32S2- 16O2- 14N3- 24Mg2+ 7Li+ 27Al3+ Exercise Worksheet - Atomic Structure of ions

Tasks Write out these Key definitions Isotopes . . Atomic ( proton ) number . . Mass ( nucleon ) number . . . An ion . . . Questions 1, 2 Examiners tips are . .

1.1.3 Atomic Masses • Explain why 12C is used as the standard measurement of relative mass. • Define the terms relative isotopic mass and relative atomic mass. • Calculate relative atomic masses. • Work out relative molecular masses and relative formula masses.

Relative Atomic Mass (Ar) RELATIVE MASSES Relative Atomic Mass (Ar) The mass of an atom relative to the 12C isotope having a value of 12.000 Ar = average mass per atom of an element x 12 mass of one atom of carbon-12 Relative Isotopic Mass Similar, but uses the mass of an isotope 238U Relative Molecular Mass (Mr) Similar, but uses the mass of a molecule CO2, N2 Relative Formula Mass Used for any formula of a species or ion NaCl, OH¯

ISOTOPES Definition Atoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons.

ISOTOPES Definition Atoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons. Properties Chemical properties of isotopes are identical Physical properties (such as density) can differ

ISOTOPES Definition Atoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons. Properties Chemical properties of isotopes are identical Physical properties (such as density) can differ Theory Relative atomic masses measured by chemical methods rarely produce whole numbers but they should do (allowing for the low relative mass of the electron). This was explained when the mass spectrograph revealed that atoms of the same element could have different masses due to the variation in the number of neutrons in the nucleus. The observed mass was a consequence of the abundance of each type of isotope. ISOTOPES OF HYDROGEN Protons Neutrons 1 H 2 3

ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms Protons Neutrons % 35 Cl 17 18 75 37 20 25

ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms Method 1 Three out of every four atoms will be chlorine-35 Average = 35 + 35 + 35 + 37 = 35.5 4 Protons Neutrons % 35 Cl 17 18 75 37 20 25

ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms Method 1 Three out of every four atoms will be chlorine-35 Average = 35 + 35 + 35 + 37 = 35.5 4 Method 2 Out of every 100 atoms 75 are 35Cl and 25 are 37Cl Average = (75 x 35) + (25 x 37) = 35.5 100 Protons Neutrons % 35 Cl 17 18 75 37 20 25

MASS SPECTRA An early application was the demonstration by Aston, (Nobel Prize, 1922), that naturally occurring neon consisted of 3 isotopes... 20Ne 21Ne 22Ne. • positions of peaks gives atomic mass • peak intensity gives relative abundance • highest abundance is scaled up to 100% - other values are adjusted accordingly. 19 20 21 22 23 m/z 90.92 0.26 8.82 Abundance / % Calculate the average relative atomic mass of neon using the above information. Out of every 100 atoms 90.92 are 20Ne , 0.26 are 21Ne and 8.82 are 22Ne Average = (90.92 x 20) + (0.26 x 21) + (8.82 x 22) = 20.179 100 Relative atomic mass = 20.18

Can we calculate the % composition if we know the isotopes ? Naturally occurring potassium consists of potassium-39 and potassium-41. Calculate the percentage of each isotope present if the average is 39.1. Assume there are x nuclei of 39K in every 100; so there will be (100-x) of 41K so 39x + 41 (100-x) = 39.1 100 therefore 39 x + 4100 - 41x = 3910 thus - 2x = - 190 and x = 95 ANSWER There will be 95% 39K and 5% 41K

Tasks Write out these Key definitions Relative isotopic mass Relative atomic mass Relative molecular mass Relative formula mass

Calculate the relative atomic mass of the following – give your answers to 3 significant figures Bromine : 79 Br 50% , 81 Br 50% Copper : 63 Cu 69% , 65 Cu 31% Zirconium : 90 Zr 51.5% , 91 Zr 11.2%, 92 Zr 17.1%, 94 Zr 17.4%, 96 Zr 2.8% Lead : 204 Pb 1.5% , 206 Pb 23.6%, 207 Pb 22.6%, 208 Pb 52.3% Neon : 20 Ne 90.9% , 21 Ne 0.2%, 22 Ne 8.9% 63.6 91.3 207. 20.2

Tasks Worksheet Exercise 1.1.3 Atomic Masses Questions : 1, 2, 3