chemical patterns exam

atom

the smallest whole particle that makes up matter

element

a substance made up of only one type of atom

compound

a substance made up of atoms of two or more different elements chemically combined

subatomic particles

protons, neutrons, and electrons

proton

positive charge, relative mass = 1amu, located in the nucleus

neutron

neutral charge, relative mass = 1amu, located in the nucleus

electron

negative charge, relative mass = 0 amu, located around the nucleus

nucleus

the heaviest part of the atom which contains positively charged protons and neutral neutrons

atomic number

the number of protons

mass number

the total number of protons and neutrons in an atom

how to calculate mass number

number of protons + number of neutrons

how to calculate neutrons

mass number - atomic number

isotopes

same number of protons, different number of neutrons

atomic mass

the weighted average mass of an element's naturally occurring isotopes

periodic table

a systematic table of all 118 known chemical elements, organised by increasing atomic number

groups on the periodic table

• vertical columns on the periodic table

• numbered 1–18

• elements have similar properties and the same number of valence electrons

periods in the periodic table

• horizontal rows on the periodic table

• Numbered 1–7

• Indicate the number of occupied electron shells

metals

• mostly solids at room temperature except mercury

• shiny with a lustre

• good conductors of heat and electricity

• ductile

• usually high melting points

non-metals

• usually dull

• brittle when solid

• cannot be bent

• usually poor conductors of heat and electricity

• usually low melting points

metalloids

• have properties of both metals and non-metals

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electron shell diagram

simplified model of an atom showing the nucleus in the middle and electrons arranged on the outer shell

valence electrons

electrons in the outer shell of an atom that are involved in chemical reactions

atomic radius

the distance from the centre of the nucleus to the edge of the electron cloud

atomic radius down a group

• increases because:

• each step down adds a new electron shell

• atoms become larger

atomic radius across a period (left to right)

decreases because the nucleus gains more protons

ion

an atom that has gained or lost electrons and therefore has an electrical charge

how do atoms form ions

atoms gain or lose electrons, this creates an imbalance between protons and electrons

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electronegativity

how strongly an atom pulls electrons towards itself in a bond

high electronegativity

An atom strongly attracts electrons

low electronegativity

an atom has a weaker attraction for electrons

factors affecting electronegativity

more protons = stronger attraction

electrons closer to the nucleus = stronger attraction

more shielding from inner electrons = weaker attraction

electronegativity across a period

increases

electronegativity down a group

decreases

ionic bonding

bonding between metals and non metals

cations

• positively charged ions

• formed when atoms lose electrons

• usually formed by metals

anions

• negativley charged ions that form when atoms gain electron

how do ionic bonds form?

• neutral atoms come near each other

• electrons transfer from the metal to the non-metal

• oppositely charged ions attract through electrostatic forces

• an ionic bond forms

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metal ions

metals form positive ions called cations

non-metal ions

non-metals form negative ions called anions

ionic compound

a compound composed of cations and anions

why are ionic compounds electrically neutral?

the total positive charge of the cations equals the total negative charge of the anions

chemical formula

shows the symbols of the elements in a compound and the ratio in which the atoms have combined

ionic lattice

a giant three-dimensional repeating arrangement of positive and negative ions

ionic bonding forces

strong electrostatic attraction between oppositely charged ions acting in all directions

are ionic compounds brittle?

yes

properties of ionic compounds

• crystalline structure

• solid at room temperature

• high melting points

• brittle

• dissolve in water to form aqueous solutions

• conduct electricity when molten or dissolved in water

covalent bond

a bond consisting of a shared pair of electrons, with one electron supplied by each atom

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how do covalent bonds help atoms achieve stability?

atoms share electron pairs rather than gaining or losing electrons to achieve a stable outer shell

bonding pair

a shared pair of electrons involved in forming a covalent bond

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top of the reactivity series

metals are very reactive and lose electrons easily

bottom of the reactivity series

metals are less reactive and lose electrons less easily

corrosion

the process where metals react with their environment and oxidise

which metals corrode more easily?

reactive metals

uses of metals based on reactivity

• low reactivity metals such as copper and gold are used for wiring and jewellery because they are stable

• high reactivity metals are used where strong reactions are needed, such as batteries

valency

the number of electrons an atom needs to gain, lose or share to achieve eight electrons in its outer shell

polyatomic ions

groups of atoms that act as one ion

polyatomic anions

groups of atoms with an overall negative charge that act as one ion

how are polyatomic ions written in formulae?

brackets around the polyatomic ion

formula mass

the sum of the atomic masses of all atoms in the chemical formula, measured in atomic mass units (amu)

how to calculate formula mass

add together the atomic masses of every atom in the chemical formula, multiplying by the number of each atom

percentage composition

the percentage by mass of each element in a compound

how to calculate percentage composition

(total mass of the element in the compound ÷ total formula mass of the compound) × 100