Chemistry Exam Revision

Describe the properties of Alkali metals

Chemical properties:

• Group 1 - have 1 valence electron, and charge of +1

• Highly reactive - readily loses 1 e to achieve a stable octet

• > reactive violently with water to form a strong alkaline base (metal hydroxide) and hydrogen gas.

Physical properties:

• Soft, low melting and boiling points

Describe the properties of Alkaline earth metals

Chemical properties:

• Group 2 - have 2 valence electron, and charge of +2

• Very reactive (not as must as Group 1) - readily loses 2 e to achieve a stable octet

• > reactive with water to form a strong alkaline base (metal hydroxide) and hydrogen gas.

Physical properties:

• Soft (harder than Group 1), low melting and boiling points (still higher than G1)

6 most reactive metals (out of 20 elements)

1. Potassium

2. Sodium

3. Calcium

4. Magnesium

5. Aluminium

6. Carbon (not metal)

Describe the properties of Transition metals

Physical properties:

• middle block in periodic table (G3 - G12)

• Some are magnetic

• Gold and Copper are the only two that are not silvery in colour

Chemical Properties:

• Many form coloured compounds

• Some have variable valencies e.g. Fe (II) and Fe (III)

Evaluates reasons for placement of transition metals in periodic table:

Reasons for placement:

• Sequential subshell filling of d-block: Positioned between Groups 2 and 13 because their d-subshells are progressively filled across the period.

• Chemical Transition: Act as a transitional bridge between highly reactive s-block metals and less reactive p-block metals.

Characteristics due to placement:

• Variable Oxidation States: The 3d subshells have the same amount of energy, allowing them to lose a variable number of electrons and form ions with different charges.

• Catalytic & Physical Traits: Their incomplete d-subshells => unique properties e.g. acting as catalysts, forming coloured compounds, and exhibiting strong magnetism.

Describe the properties of Halogens

Chemical properties:

• Group 7: 7 valence electrons, charge of -1

• Highly reactive non-metals that react with metals to form ionic salts

• Reactivity decreases down the group

Physical properties:

• the only group featuring all three states: gases (fluorine, chlorine), liquid (bromine) and solids (Iodine, Astatine) at room temperature.

• Melting and boiling points increase down the group: molecules get larger and heavier, increasing energy required to break intermolecular bonds

• exist as diatomic molecules: F2, Cl2, Br2

Describe the properties of Noble gases:

Chemical properties:

• 8 valence electrons, all have a charge of 0 as they have a complete octet (except for Helium which forms a stable duet)

• Cannot form ions, therefore are uncharged

• Are naturally inert, as they have a complete valence shell.

Physical properties:

• All colourless, odourless gases at room temp

• Exist as monatomic gases: He, Ne

• MP and BP increase down groups (atoms larger and heavier)

Explains the reactivity of alkali metals and halogens in terms of core charge and/or electronegativity

Core charge: the net positive charge experienced by valence electrons, calculated by no. of protons - no. of inner shell electrons.

Alkali metals:

• Have low electronegativity and weak core charge of +1

• The positive attraction of the nucleus over the valence electrons is weak, making it highly reactive as it is easily loses its 1 valence e.

Halogens:

• Halogens are the opposite:

• Strong core charge of +7 and high electronegativity

• Strong positive pull of the nucleus on valence electrons makes the element highly reactive - easily gains 1e to complete octet.

Explain the relationship between atomic number and placement on the periodic table:

• The atomic number determines the type of element, thus determining its organisation within the table.

• The elements are arranged, where the atomic no. increases from left to right and downwards in the periodic table.

• When a period (shell) is full, the atomic number moves to the next row, aligning elements with the same number of valence electrons into the same groups.

• Property Trends: Valence electron counts repeat in a trend as the atomic number increases, causing chemical and physical properties to recur in a pattern

Outline trends in the periodic table: atomic radii, electronegativity, 1st ionisation energy, core charge, metallic and non-metallic character, chemical reactivity

Atomic radii: the distance from the centre of the atom to its outermost shell:

• increases down the group, decreases across the period

Electronegativity: The ability of an atom to attract electrons towards itself:

• decreasing down a group, increases across a period

1st ionisation energy: The minimum amount of energy required to remove the first valence electron from its atom in gaseous state

• decreases down a group, increases across a period

Core charge: The net positive charge experienced by a valence electron (no. of protons minus no. of inner shell electrons)

• stays constant down a group, increases across a period.

Metallic character: a measure of how easily an atom becomes a cation

• LHS of periodic table

Non-metallic character: a measure of how easily an atom becomes an anion

• RHS of periodic table

What is a physical change

A changes in which the physical properties of the substance change, yet its chemical identity remains constant.

Indicators:

• reversible action

• no new chemical substances are created

e.g. shifting between different states (steam to liquid water)

What is a chemical change:

A process where a substance is transformed into a new substance with a different chemical identity, properties and rearranged chemical bonds.

Indicators:

• colour change

• effervescence

• burning

• change in odour.