Chem

• In order for a reaction to occur what must happen?

  In order for a chemical reaction to occur, reactant particles must collide with enough energy & correct orientation.
• What are catalysts?


  Catalysts are substances that speed up chemical reactions but can be recovered chemically unchanged at the end of a reaction.
• How can rates of reactions be increased?

  decreasing particle size❌ (which) increases surfcae area✅
• To follow the progress of a chemical reaction, what different measurements can we take?

  the changes in;

  - mass of reactants or products

  - volume of reactants or products
• How can you measure the change of volume of a gas and mass loss in a reaction?

  Mass loss;

  - mass loss in a beaker beaker is on a scale, there is a reaction going on, the top is covered in cotton wool to only allow gas to escape, the weight changes as the gas escapes
• Understanding graphs- What is the rate? What is the end point?

  End point- when a line graph becomes flat (horizontal) this tells us that the reaction has finished.

  Rate- gradient of the graph
• How can we calculate the average rate of a chemical reaction?

  rate= change in quantity

  ___________________

  change in time
• How can you show the reaction decreasing over time?

  By calculating the average rate at different stages of the reaction.
• How are elements in the periodic table arranged?

  Elements in the periodic table are arranged in order of increasing atomic number (& chemical properties).
• What do elements in groups have the same of and similar?

  Elements within a group share the same valency and have similar chemical properties
• What are Group 1, Middle block, Group 7 and Group 8 all called and what are their reactivities?

  Group 1- Alkali metals, Very reactive Metals

  Middle block- Transition metals

  Group 7- Halogens, Reactive Non-Metals

  Group 0- Noble Gases, Unreactive Non-Metals
• What are atoms made up of?

  An atom has a nucleus, containing protons and neutrons, and electrons which orbit the nucleus.
• What are the masses and charges of a proton, neutron and electron?

  Mass Charge

  Proton 1 +1

  Neutron 1 No charge (neutral)

  Electron Virtually no mass -1
• Why is an atom neutral?

  Number of protons = Number of electrons
• What is the valency of an element?

  Group Valency

  1 1 They have to lose 1 electron meaning the charge will be +1

  2 2 They have to lose 2 electrons meaning the charge will be +2

  3 3 They have lose 3 electrons meaning the charge will be +3

  4 4 They have to lose or gain 4 electrons meaning the charge will be +4 or -4

  5 3 They have to gain 3 electrons meaning the charge will be -3

  6 2 They have to gain 2 electrons meaning the charge will be -2

  7 1 They have to gain 1 electron meaning the charge will be -1

  8/0 0 They do not have to gain or lose any electrons as their outer electron shell is full.
• If the number of protons changes what happens?

  The atom becomes a different element
• What is the summary of an element?

  Atomic number = Number of protons in an atom

  Mass number = Number of protons + netrons

  Number of neutrons = Mass number - Atomic Number
• What are isotopes? Why is this possible?

  Nuetrons have mass, which means atoms of the same element with have the same atomic number (number of protons) but different mass numbers (number of neutrons)
• What can most elements have?

  Most elements will have 2 or more isotopes.
• How can nuclide notation be used? Example

  Mass number is always on the top.

  Atomic number is always on the bottom.

  Mass number = 35

  Atomic number = 17 (so this means)

  Protons = 17

  Electrons = 17

  Neutrons = Mass number - Atomic Number = 35 - 17 =18
• How can the average atomic mass be calculated? Example

  The average atomic mass is between 35 and 37 and 35.5 is closer to 35.

  35 Cl is more abundant than 37 Cl.
• What are the Noble Gases?

  Meaning, they are very unreactive and exist as single atoms, do not form bonds; monatomic elements.
• What is a covalent bond?

  Covalent bond is a bond that forms between non-metals when 2 positive nuclei are held together by their common attraction for a share pair of electrons.
• What are the 7 diatomic elements and what are they?

  I2- Iodine

  Br2- Bromine

  Cl2- Chlorine

  F2- Flourine

  O2- Oxygen

  N2- Nitrogen

  H2- Hydrogen
• What does the shape of covalent molecules depend on and what can they be decribed as?

  Angular:

  O

  / \

  H H = H2O
• How many covalent bonds can be formed between atoms?

  More than 1 bond can be formed between atoms- double and triple covalent bonds
• Describe covalent molecular substances

  Have low melting and boiling points as only weak forces of attraction between the molecules are broken when a substance changes state
• What are covalent molecular substances?

  Discrete molecules- Small covalent molecules with low melting & boiling points as there is only weak attractions betweeen the molecules which are broken when a substance changes state. This is because the molecules are futher apart and free to move.
• Fill in the blanks: Some covalent substances such as ... & ... are ... in ... and will dissolve to form a ...

  Some covalent substances such as sugar & chorine are soluable in water and will dissolve to form a solution.
• Fill in the blanks: Other covalent molecular substances such as ... are ... in water but are ... in other covalent substances e.g. nail varnish will ... in ...

  Other covalent molecular substances such as nail varnish are insoluble in water but are soluble in other covalent substances e.g. nail varnish will dissolve in acetone.
• What are different covalent molecular and compound states at room temperature?

  Compounds:

  Many compounds also exist in different states at room temp e.g.

  - Sugar = solid

  - Water = liquid

  - Methane = Gas
• Describe covalent networks


  Do not conduct electricity because they do not have charged particles which are free to move except graphite
• What is a covalent network?

  A network of strong covalent bonds within 1 giant structure and very high melting & boiling points because the networks are not easily broken
• What are 3 examples of covalent networks and their properties?

  Graphite, Covalent network of carbon, soft, slippery, lead in pencils. Graphite can conduct because it has 1 free electron which does not form a covalent bond, this free electron can carry charge and move between layers of carbon atoms.
• What are ions?


  Ions are charged particles which are formed when atoms lose or gain electrons to obtain the stable electron arrangement- full outer energy level- of a Group 0- Noble Gas.
• What happens if an atom loses or gains an electron?

  Atom gains electrons —> Negative ion
• Describe transition metal ion

  Most transition metals can make more than 1 type of ion by losing different numbers of electrons. The electrons lost is in roman numerals after the name e.g.
• What are group ions?


  Group ions= ions that contain more than 1 type of atom e.g.
• What is ionic bonding?

  Ionic bond= the electrostatic attraction between positive and negative ions it is a bond that forms between a metal and a non-metal where 1 or more electrons are transferred from the metal ion to the non-metal atom to form charged ions with full outer electron shells.
• What is an ionic lattice?

  Lattice: the structure formed by ionic compounds consisting of oppositely charged ions- each positive ion surrounded by negative ions and each negative ion surrounded by positive ions.