Chapter 2: Atoms, Ions and compounds

Proton: relative mass 1 charge +1 Neutron: relative mass 1 charge 0 Electron: Relative mass 1/1836 charge -1

Top (bigger) number - mass number (A) Bottom (smaller) number - Atomic number (Z) Letters- element symbol

Atoms OF THE SAME ELEMENT with the same number of protons (Z), but different isotopic mass due to different number of neutrons.

Mass number: the sum of protons and neutrons Atomic number: the number of protons

• 3 subatomic particles: proton, neutron, electron • small nucleus and large (empty) space around it • protons (positive charge) and neutrons (neutral charge) found in the nucleus • electrons (negative charge) found orbiting space around nucleus • For a neutral atom, the number of electrons is equal to the number of protons

Neutrons can be thought of as providing the glue that holds the nucleus together despite the electrostatic repulsion between positively charged protons. Also, as the nucleus gets larger, more and more neutrons are needed

TRICK QUESTION • Isotopes of the same element have the same number of electrons • Number of neutrons has no effect on the reactions of an element • so different isotopes therefore react in the same way However, there are small differences in physical properties- with higher-mass isotopes of an element having a higher melting point, boiling point, and density - but the chemical reactions are the same.

Heavy water is used to control processes in nuclear reactors. Heavy water: 2 1H isotope of hydrogen aka deuterium with its own symbol D (D2O) Super heavy water: 3 1H isotope, aka Tritium, T (T2O)

• Positive ions, or cations, are atoms with fewer electrons than protons - OVERALL POSITIVE CHARGE • Negative ions, or anions, are atoms with more electrons than protons - OVERALL NEGATIVE CHARGE

Ions and atoms of an element have the SAME number of protons but a DIFFERENT number of electrons.

The WEIGHTED MEAN mass of an ATOM of an element, compared to 1/12th of the mass of an ATOM OF CARBON-12.

The mass of an atom of an isotope, compared to 1/12th of the mass of an atom of carbon-12.

1dp

(mass no. isotope 1 * abundance) + (mass no. isotope 2 * abundance ) / 100 (or total abundance)

• To find relative isotopic masses • To find the relative abundance of the different isotopes • To find the relative atomic mass of the element

• Samples of elements or molecules are vaporised. • Vapour is bombarded with high energy electrons which knock out electrons to produce positive ions. • Positive ions are accelerated by an electric field (heavier ions move more slowly than lighter ions so are more difficult to deflect and so ions of each isotope are separated). • Ions are deflected by a magnetic field. • Ions deflected by a particular combination of electric/magnetic fields are detected. The magnetic field is varied until all ions are detected. The ions are detected as a mass-to-charge ratio.

Relative mass of ion / relative charge on ion

Turning a substance into a gas.

Atoms on the left (ie metals) lose electrons to form cations (positive ions) Atoms on the right (ie non metals) gain electrons for form anions (negative ions)

A binary compound contains TWO elements only. Eg. sodium oxide

Ions that contain atoms of more than one element bonded together.

Ammonium: NH4+, hydroxide OH-, carbonate CO32-, hydrogencarbonate HCO3-, sulphite SO32-, sulphate SO42-, thiosulphate S2O32-, tetrathionate S4O62-, nitrite NO2-, nitrate NO3-, cyanide CN-, phosphate PO43-, hypochlorite / chlorate (I) ClO-, chlorate (V) ClO3-, dichromate CrO72-, manganate (VII) or permanganate MnO4-

Diatomic molecule: molecule containing two atoms bonded together. H2 N2 O2 F2 Cl2 Br2 I2 P4 S8

Ag+, Sn2+, Pb2+, Zn2+