Chemistry Flashcards
When is an ionic bond formed?
By transfer of electrons from METAL atoms to the more electronegative NON-METAL atoms
Cations
Metals form cations, cations have an overall positive charge as they lose electrons (low electronegativity)
Anions
Non-metals form anions, anions have an overall negative charge as they gain electrons to obtain a stable outer shell (higher electronegativity)
Electronegativity
The ability of an atom to attract electrons
Electrovalency
The charge value of an ion (e.g beryllium has 2 electrons in outer shell, to have a stable outer shell beryllium will lose 2 electrons to form a Be2+ ion, therefore electrovalency of beryllium is 2+) - gaining electrons means negative electrovalency
Ionic Bonding
The complete transfer of valence electrons between atoms. For example one electron is removed from the valence shell of sodium and accepted by the chlorine atom into its valence shell. Sodium ion (Na+) and chloride ion (CI-), meaning there is an electrostatic attraction (+ and - attracted). As a result sodium chloride (NaCI) is formed.
Monoatomic ions
Ions that are made up of one atom e.g. sodium ion Na+
Polyatomic ions
Ions that are made up of more than one atom e.g. nitrate ion NO3-
Covalent bonding
Molecules are formed between a NON-METAL and a NON-METAL (bond is formed by the sharing of electrons)
Single bonds
When a bond is formed by the sharing of two electrons (single covalent bond)
Double bonds
Sharing a total of four electrons (or two pairs of electrons), double covalent bond
Triple bonds
Sharing of total of 6 electrons (or three pairs of electrons) e.g. two nitrogen atoms, each shares three electrons with the other
Octane rule
The octane rule identifies that atoms are most stable when they have eight electrons in their valence shell
Electronegativitiy of non-metals (high or low)
Non-metals have high electronegativities so they can attract electrons easily, but don’t give up electrons easily
Bonding electrons
electrons shared between the atoms
Non-bonding electrons
the outer shell electrons not involved in forming a bond (lone pairs).
What happens when a chemical reaction occurs?
The atoms rearrange (change places)
Signs of chemical change
- Colour change
- Gas produced (bubbles)
- A solid (precipitate) forms in a solution
- Energy is produced or absorbed in the from of heat, sound or light
Law of conservation of mass
States that matter cannot be created or destroyed, but it can change forms. (Meaning the number and type of atoms must be the same for both reactants and products)
Exothermic reactions
Chemical reactions that release energy into the surroundings, surroundings are warmer as a result. E.g. burning fuel (product energy is less than energy in reactants, released)
Endothermic reactions
Chemical reactions that absorb energy from the surroundings, surroundings are colder as a result E.g. test-tube feels cold (product energy is greater than energy in reactants, absorbed)
4 Classes of Chemical Reactions
- Decomposition reactions
- Synthesis reactions
- Single displacement reactions
- Double displacement reactions
Decomposition reaction
AB—> A+B (when a single compound breaks down into two or more elements or new compounds)
Synthesis reaction
A + B—> AB (When two reactants combine to form one product)
Single Displacement Reaction
AB + C —> A + BC (when an element reacts with a compound and takes the place of another element in that compound)
Double Displacement Reactions
AB +CD —> AD + CB (when two compounds react, the positive cation and the negative anion of the two reactants switch places, forming two new substances)
Type of Double Displacement: Precipitation Reactions
A precipitate reaction is when soluble aqueous solutions react to form an insoluble solid called a precipitate. (solubility rules determine whether a reaction will form a precipitate)
Soluble
DISSOLVES (aq)
Insoluble
DOES NOT DISSOLVE (s)
Combustion
Combustion reactions are those in which a substance reacts with oxygen, and heat is released (General equation= Hydrocarbon + oxygen —> Carbon dioxide + water (+ heat and light))
Hydrocarbons
Compounds containing only the elements carbon and hydrogen e.g. methane CH4, ethane C2H6
Neutralisation Reactions
When an acid and a base react with each other to produce water and a salt (General equation: Acid + Base —> Water + Salt)
How is the salt formed in a neutralisation reaction?
Combine cation (written first) from base and anion (written second) from acid e.g. base sodium hydroxide reacts with sulfuric acid creating sodium sulfate THEN USE IONS CHART to balance charges
What are indicators used for?
Used to identify when the neutralisation between an acid and base is complete (the end point is reached when the solution changes colour)
