chem exam easy memorisation sem 1

difference between physical and chemical changes.

physical- no new substance is formed ( easy to reverse usually) chemical- new substance is formed (not easy to reverse usually)

chemical change signs

evervescenece, colour change, temperature change, electricity produced, precipitate formed, new substance is formed, sound or light produced

ionic combinations

1 and 17, 2 and 16 group elements

chromate

cro4 2-

dichromate

cr2o7 -

cyanide

cn-

nitrate

no3 -

nitrite

no2 -

oxalate

c2o4 2-

permanganate

MnO4-

peroxide

o2 2-

hydrogenphosphate

HPO4 2-

dihydrogenphosphate

H2PO4 -

hydrogensulfate

HSO4 -

systematic naming exceptions

Water, Hydrogen Peroxide, Ammonia, Methane, Nitrous Oxide, Nitric Oxide, Ozone

group 18

noble gases (monamotic elements)

diatomic elements

ex. H2, O2, N2, Cl2

polyatomic elements

ex. P₄, S₈.

atoms

modelled as a dense, positively charged nucleus consisting of protons and neutrons surrounded by electrons in distinct energy levels, held by electrostatic forces of attraction between the nucleus and electrons.

molecules

consists of two or more atoms CHEMICALLY bonded together. The atoms in the molecule can be the same (element) or different (molecule)

how are chemical bonds formed

the ability of atoms to form chemical bonds are explained by the arrangement of electrons in the atom and in particular by the stability of the valence electron shell. Caused by electrostatic attractions that arise because of the sharing (covalent) or transfer of electrons between participating atoms (ionic).

differences with isotopes

atoms of an element with the same number of protons but different numbers of neutrons. have different physical properties.

similarities with isotopes

same electron confiugaration and posses similar chemical properties. They possess similar chemical properties because electrons are the sub-atomic particles that are primarily responsible for chemical properties because they are the most easily lost or gained particle

physical property differences (isotopes)

Colour, melting point, boiling point, density, solubility in water

relative atomic mass

A_r is the ratio of the average mass of the atom to 1/12 the mass of an atom of ¹²C; relative atomic masses of the elements are calculated from their isotopic composition.

Calculate the relative atomic mass given the isotopic mass and relative abundances of the isotopes of an element.

• Bromine is made up of two isotopes, Br-79 and Br-81. Given bromine's atomic weight of 79.90, what is the percent abundance of each isotope?

• Chlorine is made up of two isotopes, Cl-35 and Cl-37. Given chlorine's atomic weight of 35.45, what is the percent abundance of each isotope?

Br-79 (55%) and Br-81 (45%), Cl-35 (77.5%) and Cl-37 (22.5%)

How is the degree of deflection related to charge and to the mass of a charged species in mass spectrometry.

low mass and high charge (largest deflection)

emission spectra

When chemicals are heated, electrons will absorb energy and go into a higher energy shell (orbital). This is an unstable electron configuration and the electron is said to be in an “excited” state. It will very quickly fall back down releasing this energy as light.

uses of emission spectra

A flame test is a qualitative analytical procedure used to detect the presence of certain elements, usually metal ions, based on the element’s emission spectrum. It can’t detect the quantity present.

matter

anything that has atoms and takes up space

elements

• identified by its atomic number (determined by number of protons)

• mass number (total number of protons and neutrons in the nucleus of atom)

• elements are pure substances (constant composition)- cannot be separated into simpler substances;

• e.g. au

compounds

compounds are pure substances (constant composition) two or more elements that are chemically combined in a fixed ratio e.g. H20

homogenous mixtures (physically combined)

solutions- uniform composition and properties throughout e.g. NaCl

heterogenous mixtures (physically combined)

variable composition and properties throughout e.g. sandy seawater

decantation

solution lying above a sediment is poured very gently away from the sediment.

filtration

process by which an undissolved solid is separated out of a suspension by passing it through filter paper in a filter funnel.

The solid that is trapped in the filter paper is called the residue and the solution that passes through the paper is called the filtrate.

method determined by patricle size

crystallisation

The process of forming crystals, usually by evaporating the filtrate to dryness. This is used to separate a dissolved solid from a solution. method determined by solubility diffrences

distillation

method depends on the components having different boiling points. It is commonly used in the purification of liquids.

fractional distillation- when there is a mixture of liquids e.g. petroleum