Chemistry Spaced Repetition Exam Sem 1

Explain the differences between physical and chemical changes.

Physical change forms no new substance but chemical change does

State the signs of a chemical change

Colour, melting/boiling point, new substance formed, effervescence (bubles of gas produced), precipitate (solid is formed in solution) produced, temp change, electricity produced, light or sound may be produced

Ite ions

Non-metal ions combined with oxygen but have usually one less than ate ion

Ionic bonding

Bonding in compounds containing elements from Groups 1 or 2 of the Periodic Table combined with Groups 16 and 17 is ionic.

Covalent bonding

Covalent compounds formed when electrons are shared between elements on the right-hand side of the Periodic Table combine with other elements including Hydrogen on the right hand side of the Periodic Table. Use systematic naming to indicate how many of each element are present in covalent compounds.

Systematic Naming Rule

Prefix for first element (only if there is more than one atom), always prefix for second element

Exceptions of Systematic Naming

Water, Hydrogen Peroxide, Ammonia, Methane, Nitrous Oxide (dinitrogen monoxide), Nitric Oxide (nitrogen monoxide), Ozone (O3)

Atoms

Modelled as a dense positively charged nucleus consisting or protons and neutrons (element’s mass number), surrounded by negatively charged electrons in distinct energy levels, held together by electrostatic forces of attraction between the nucleus and electrons. There are an equal number of protons to electrons.

Relative charges of sub-atomic particles

p- +ve (mass of 1), neutral-0 (mass of 1), e- -ve (mass of 0)

Purpose of valence electrons

Valence electrons are involved in electron transfer or sharing to achieve a stable electron arrangement

Valency

The measure of an atom's ability to bond with other atoms to form chemical bonds determined by the arrangement of electrons in the atom and in particular by the stability of the valence electron shells. The number of valence electrons in valence shell.

Why chemical bonds occur?

Chemical bonds are caused by electrostatic attractions that arise because of the sharing or transfer of electrons between participating atoms.

What do the main groups of the Periodic Table represent

Represent elements with similar chemical properties and the same number of valence electrons.

How can chemical properties of elements be predicted on Periodic Table?

Observing an element’s main group position on the Periodic Table indicates their valence electron configuration and similarities in reactivity.

Periods of the Periodic Table

Represent the number of occupied electron shells

Atomic Number

Determines the number of protons, hence atom (and electrons in neutral atom)

Mass Number

Total number of protons and neutrons in the nucleus of an atom.

Isotopes of Atoms

Atoms of an element with the same number of protons but different numbers of neutrons, hence resulting in different atomic masses

Isotopes of Elements

Have the same electron configuration and possess similar chemical properties but have different physical properties due to differences in atomic masses. Ex. there is a small increase in melting point in the heavier isotopes

Physical behaviours of an isotope

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

What determines chemical properties of isotopes and why?

Electrons- The chemical behavior of isotopes is determined by electron configuration and stability

Differences in physical properties of isotopes of the same element

Colour, melting point (ex. Hydrogen Isotopes), boiling point, density, solubility in water

Define relative atomic mass (atomic weight)

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.

Explain the existence of fractional atomic masses of some elements in terms of the existence of naturally occurring isotopes.

Occur due to the presence of isotopes of an element, as each isotope has a different mass. The average atomic mass is calculated based on the relative abundances and masses of these isotopes

Mass Spectrometry Process

Draw Diagram

Purpose of Mass Spectrometer

Involves the ionisation of substances and the separation and detection of the resulting ions; the emmision spectra which are generated can be analysed to determine the isotopic composition of elements and interpreted to determine relative atomic mass

Flame Test

Analytical procedure used to detect the presence of certain elements, usually metal ions, based on the element’s emission spectrum. Flame reacts to chemical that is being heated and takes on colour of that chemical (after absorption spectrometry occurs)

Purpose of Atomic Absorption Spectroscopy (AAS)

AAS is a procedure used for the quantitative determination of chemical elements using the absorption of light by free atoms in the gas phase.

Describe how atomic absorption spectroscopy (AAS) is used to identify elements.

A lamp emits a beam of light from excited atoms of a known element. Radiated light is only absorbed by an atomised sample of groundstate free atoms in a gaseous state that contains lamp element. This is because atoms of different elements will emit and also absorb characteristic and unique wavelengths of light. The amount of light absorbed is proportional to the concentration of known element in sample.

Describe the use of AAS in detecting concentrations of metal ions in solutions.

Calibration Curve- running several samples of a concentration of known element under the same conditions as the sample we are testing. We then compare the amount the unknown atomised sample absorbs to our calibration curve and we can calculate the concentration of known element