Chemical Patterns and Reactions

Nucleus

The centre of an atom, which contains protons and neutrons, and accounts for the mass of the atom. The nucleus has an overall positive charge.

Protons

The number of protons determines the element.

• positive charge,

• have a mass

• located in the nucleus.

Are attracted to electrons.

Known as subatomic particles

Neutrons

• no charge (neutral)

• located in the nucleus.

  Known as subatomic particles

Electrons

• negative charge

• no mass (1840th of a proton and neutron)

• orbit the nucleus (in shells/orbitals)

Are attracted to protons. The closer the electrons are to the nucleus, the greater the attraction to the protons will be.

Known as subatomic particles

Electrons in the same shell are the same radium from the nucleus.

Atom

The smallest particle of a substance, that can still be that substance. They compose all matter.

Atomic number

Equal to the number of protons

Mass number

Equal to the number of protons and neutrons in an element

Isotopes

Atoms with the same number of protons, but different number of neutrons, so atoms of the same element have different mass numbers.

Ions

Atoms that have a positive or negative charge.

Valence electrons

Electrons in the valence shell (which can never have more then 8 electrons)

Valence electrons are the ones involved in chemical reactions.

Cations

A positively charged ion (it loses electrons)

Anions

A negatively charged ion (it gains electrons)

Octet Rule

Atoms prefer to have 8 electrons in their outer shell, to be as stable as possible

Periods

Horizontal rows on the periodic table.

Numbered 1-7

Elements in the same period have the same number of shells containing electrons.

eg. all atoms in period 4, have 4 shells

Groups

Vertical columns on the periodic table.

Numbered 1 - 18

Elements in the same group, have the same number of valence electrons in the outer shell, therefore they have similar chemical properties.

Alkali metals

• Group 1 elements are alkali metals

• They are highly unstable

• Reactivity increases further down the columns

• Have a +1 charge as ions

Alkaline earth metals

• Group 2 elements are alkaline earth metals

• They are highly unstable

• Reactivity increases further down the columns

• Have a +2 charge as ions

Halogens

• Group 17 elements are halogens

• Unstable

• Reactivity increases higher up the column

• Have a -1 charge as ions

Noble gases

• Group 18 elements

• Stable (full valence shell)

• Highly un reactive (full valence shell)

• Exist as single atoms

Atomic radius

The distance from an atom’s nucleus to the valence shell

• The smaller the atomic radius, the stronger the attraction, and the higher the reactivity

Reactivity

A substances tendency to chemically react with another substance

Metals

• Solid at room temperature (except for mercury)

• Conducts heat and electricity proficiently

• Generally hard but brittle

• Malleable and ductile

• Lustrous

• High melting point

Non-metals

Essentially the opposite of metals

• Poor conductors of heat and electricity

• Dull, brittle, unmalleable

• Low melting point (generally gases at room temperature)

Metalloids

Behave like metals, and non-metals (semi-conductors)

Transition metals

• Similar properties to main group metals

• Groups 3-12

Ionic bonding

• Occurs between a metal and non-metal

• The atom will lose or gain electrons with another atom, so a cation and anion are formed

• The metal becomes stable by giving away its valence electrons (cation +)

• The non-metal gains the electrons the metal loses (anion -)

• Both the atoms will now have full, and therefore stable valence shells

• This cation and anion have opposite charges to one another (eg 2+, 2-) so the net charge will be 0

• These opposite charges (cations and anions) are strongly attracted to one another, which bonds the atoms

• No electrons are lost in ionic bonding, rather they are just transferred.

Molecules

Two or more bonded atoms.

Lattice

The continuous arrangement of bonded atoms in regular patterns.

Ionic lattices are held by electrostatic attraction, and they form hard, rigid, and brittle substances (crystals).

Ionic substances

• Do not conduct electricity as solids

• Conduct electricity in molten states

• High melting point

Electron transfer diagram

A diagram that represents the transfer of electrons during ionic bonding between atoms.

• include electrical configuration

• include charges (for ions)

• include arrows to show the transfer of electrons

Ionic formula

• Ensure that the net charge is 0

• Do NOT write the charges in the formula

• If the amount of a molecule is being changed, then the molecule must be put in brackets to ensure that the subscript applies to the entirety of it

• The name of the metal does not change

• The name of the non-metal does change

• If it is a singular element and ‘IDE’ is added (eg. chlorine become chloride)

• If the non-metal is a compound itself, then the name does not change (eg. sulfate, carbonate)

Metallic bonding

• Occurs between a metal and a metal

• Metals become cations

• Metals have the structure of being a layer of cations surrounded by a sea of delocalised electrons

• The cations are arranged in a closely packed structure

• While the delocalised electrons are free to move throughout the lattice, belonging to the lattice as a whole.

• They are held in the lattice through electrostatic forces of attraction

• The net charge is 0

Metallic substances

• Have the properties of metals

• These properties are explained through metallic bonding

• Electricity conductor: the delocalised electrons carry the current from negative to positive

• Heat conductor: the electrons vibrate to transfer energy, and when heated, they vibrate more

• Lustrous: the delocalised electrons reflect heat

• Malleable and ductile: the layer of cations can be forced across each other

• High melting and boiling points: Large amounts of heat energy must be applied to break the electrostatic attraction

• Dense: closely packed structure

Covalent bonding

• Occur between a non-metal and non-metal

• The octet rule is fulfilled by atoms sharing their valence electrons with one another.

• These shared electrons become the “glue“ that keeps the atoms bonded

• One of the strongest bonds in chemistry

• Certain non-metals always exist as a pair of atoms (eg.H2, O2, F2)

Covalent substances

• Low melting and boiling point: because the bond has to broken, rather then intermolecular forces

• Are liquids or gases at room temperature

• Do not conduct electricity

Lewis diagram/electron dot diagram

• Paired electrons are referred to as “lone pairs” (or non-bonding electrons)

• Bonded electrons are referred to as “bonded electrons”

• Used to covalent molecules

• The atom with the most bonding electrons is placed in the middle

• Except for hydrogen, all atoms must have 8 electrons around them

• All electrons will share as many electrons as they need to gain

Valence structures

• Another representative of covalent molecules

• Each shared pair of electrons is replaced by a dash

Forumla names

Prefixes are applied to convey information about the number of atoms in each molecule of a non metal’s name.

State symbols

• solid (s)

• liquid (l)

• aqueous (aq)

• gas (g)

Chemical reactions

Reaction during which atoms are rearranged, so that the products are not the same as the reactants

Chemical change must occur, in the formation of a new chemical product

Reactants

Chemicals pre reaction

Products

Chemicals post reaction

Law of Conversation of Mass

• Hinges on the principle that matter cannot be destroyed or created, only rearranged

• So during a chemical reaction, atoms are just rearranged

• Therefore mass cannot be created or destroyed

• So the mass of the reactants will be equal to the mass of the products

Law of Constant Proportions

Some chemicals will always exist in certain proportions (rations)

Chemical equations

• Are balanced when the reactants are equal to the products

• Chemical equations are balanced when the Law of Conversation of Mass is satisfied

• Equations can only be balanced by changing the coefficient

• The subscript can never be changed

• reactants > products

  1. Write the word equation

  2. Write the chemical formula of each substance (include states)

  3. Balance the equation

Combination reactions

• AKA synthesis reaction

• Two chemical reactions form one product

• A + B > AB

Decomposition reactions

• One reactant forms several products

• AB > A + B

Precipitation reactions

• A and C, two cations react with B and D, two anions

• These two aqueous substances produce an aqueous substance, and a precipitate

• AB (aq) + CD (aq) > CB (aq) + AD (s)

Precipitate

An insoluble, solid compound

Solubility

Whether a substance can be dissolved into water

Determined via a solubility table