ATOMICSTRUCTURE

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

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

THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are... Mass / kgCharge / C Relative mass Relative charge PROTON NEUTRON ELECTRON Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons x x x x x

THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are... Mass / kgCharge / C Relative mass Relative charge PROTON NEUTRON ELECTRON Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons x x x x x x x x x x x =

THE STRUCTURE OF ATOMS Atoms consist of a number of fundamental particles, the most important are... Mass / kgCharge / C Relative mass Relative charge PROTON NEUTRON ELECTRON Calculate the mass of a carbon-12 atom; it has 6 protons, 6 neutrons and 6 electrons x x x x x x x x x x x = x 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 Na Mass Number (A) PROTONS + NEUTRONS 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 Na Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS THESE ALWAYS GO TOGETHER – ANYTHING WITH 11 PROTONS MUST BE SODIUM

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 Na Mass Number (A) PROTONS + NEUTRONS 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 Na Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS THERE WILL BE 12 NEUTRONS IN THE NUCLEUS 23 – 11 = 12

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 Na Mass Number (A) PROTONS + NEUTRONS Atomic Number (Z) PROTONS

MASS NUMBER AND ATOMIC NUMBER ProtonsNeutronsElectronsCharge Atomic Number Mass Number Symbol A B20040 C+1123 D660 E F613 G H 27 Al 3+

MASS NUMBER AND ATOMIC NUMBER ProtonsNeutronsElectronsCharge Atomic Number Mass Number Symbol A K B Ca C Na + D C E U F C G S 2- H Al 3+

The Octet Rule The “goal” of most atoms (except H, Li and Be) is to have an octet or group of 8 electrons in their valence energy level. They may accomplish this by either giving electrons away or taking them. Metals generally give electrons, nonmetals take them from other atoms. Atoms that have gained or lost electrons are called ions.

Ions When an atom gains an electron, it becomes negatively charged (more electrons than protons ) and is called an anion. In the same way that nonmetal atoms can gain electrons, metal atoms can lose electrons. They become positively charged cations.

Ions Here is a simple way to remember which is the cation and which the anion: This is a cat-ion. This is Ann Ion. He’s a “plussy” cat! She’s unhappy and negative. +

Cation Formation 11p+ Na atom 1 valence electron Valence e- lost in ion formation Effective nuclear charge on remaining electrons increases. Remaining e- are pulled in closer to the nucleus. Ionic size decreases. Result: a smaller sodium cation, Na +

Anion Formation 17p+ Chlorine atom with 7 valence e- One e- is added to the outer shell. Effective nuclear charge is reduced and the e- cloud expands. A chloride ion is produced. It is larger than the original atom.

An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5

A monatomic ion contains only one atom A polyatomic ion contains more than one atom 2.5 Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -

Monoatomic Anions Monoatomic anions are named by adding the suffix -ide to the stem of the name of the nonmetal from which they are derived. e.g. N 3- nitrideO 2- oxide H - hydrideS 2- sulfide F - fluorideSe 2- selenide Cl - chlorideTe 2- telluride Br - bromideI - iodide

Multiple Polyatomic Ions When a nonmetal forms two oxoanions, the suffix -ate is used for the anion with the larger number of oxygen atoms. The suffix –ite is used for the anion containing the fewest number of oxygens. When a nonmetal forms more than 2 oxoanions, the prefixes per- (largest number of oxygen atoms) and hypo- (fewest oxygen atoms) are used.

Trends in the Formation of Ions of the Main Group Elements Group No. of Electrons in Atom Charge Examples 1 1 more than noble gas +1 Na, K 2 2 more than noble gas +2Mg, Ca 16 2 less than noble gas -2O, S 17 1 less than noble gas -1 F, Cl

Metals With Multiple Valences In order to distinguish between these different ions, a roman numeral is used to indicate the charge e.g. Fe 2+ iron(II)Fe 3+ iron(III) An older system uses the endings –ic for the ion of higher charge and –ous for the ion of lower charge. e.g. Fe 2+ ferrousFe 3+ ferric

13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in Al ? 3+3+ How many protons and electrons are in Se ?

RELATIVE MASSES Relative Atomic Mass (A r ) The mass of an atom relative to the 12 C isotope having a value of A r =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 238 U Relative Molecular Mass (M r ) Similar, but uses the mass of a moleculeCO 2, N 2 Relative Formula Mass Used for any formula of a species or ionNaC l, OH¯

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

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

ISOTOPES DefinitionAtoms with… the same atomic number but different mass number or the same number of protons but different numbers of neutrons. PropertiesChemical properties of isotopes are identical Physical properties (such as density) can differ TheoryRelative 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. ProtonsNeutrons 1 H H H 1 12 ISOTOPES OF HYDROGEN

ISOTOPES - CALCULATIONS There are two common isotopes of chlorine. Calculate the average relative atomic mass of chlorine atoms ProtonsNeutrons% 35 Cl Cl

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 = = ProtonsNeutrons% 35 Cl Cl

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 = = Method 2 Out of every 100 atoms 75 are 35 Cl and 25 are 37 Cl Average = (75 x 35) + (25 x 37) = ProtonsNeutrons% 35 Cl Cl

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

MASS SPECTRA Naturally occurring potassium consists of potassium-39 and potassium-41. Calculate the percentage of each isotope present if the average is Assume there are x nuclei of 39 K in every 100; so there will be (100-x) of 41 K so 39x + 41 (100-x) = therefore 39 x x = 3910 thus - 2x = and x = 95 ANSWER There will be 95% 39 K and 5% 41 K

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