C3 + C4 Flashcards
Define chemical change
Change that involves a chemical reaction and creates a new chemical substance
Difficult to reverse
Energy out (exothermic) or in (endothermic)
What are some example words of chemical change
Burning , cooking, rusting, rotting decomposing
Define physical change
Change that changes the form but not the chemical identity (no new chemical substance)
Can be reversible with enough energy
What are some example words of physical change?
Boiling, melting, freezing, shredding
What are some examples of how chemical reactions can be reversed? (Anhydrous and hydrated copper (II) sulphate and cobalt (II) chloride)
Some chemical reactions can be reversed by changing reaction conditions
Heating hydrated copper sulphate (blue crystal) -> anhydrous copper sulphate (white powder) -> wetting -> back to hydrated
Same for cobalt chloride
Hydrated -> purple
Anhydrous -> blue
Describe (or draw) the structure of an atom including the characteristics of electrons, protons and neutrons
Nucleus -> center of the atom and contains protons and neutrons
Dense (basically all of mass)
Positively charge (portons and neutrons)
- protons -> positively charged (1AMU)
- neutrons -> no charge (1 AMU)
Electrons
Negative charge (around 0 AMU)
Small
Create shell/spread out around nucleus
Lost or gained during chemical reactions
Describe the build up of electrons in shells
Each shell can hold a different number of electrons -> 2n^2
If one level full -> electrons go to next level
If a shell a incomplete -> reactive
- one or two -> very reactive
Why are noble gases electron structure ‘unique’?
Their shells are full, so they are unreactive
Define atomic/proton number
The number of protons in a nucleus
Define the mass/neucleon number
Total number of protons and neutrons in the nucleus (can account for isotopes)
What are the rows on a periodic table called? What are they based off of?
Periods
Based on the proton numbers
Proton number goes up as you along
Add proton -> change element
Define isotopes
Atoms of the same element which have a different number of neutrons and therefore a different nucleon number
Same atomic, different mass
- same properties because same electron number
- chemically identical
- can effect physical properties
How are ions formed?
Atoms can become more stable by losing or gaining an electron (gain full outer shell) when reacting with other atoms
Ions -> atoms with electrical charge
Cation -> lose -> positive
Anions -> gain -> negative
What parts of the periodic table usually form cations and anions?
Cations -> most metals
Anions -> most nonmetals
Why are transition metals special (ions)?
Most transition metals have multiple ions
Although there are exceptions:
Silver
Zinc
Ex: Cu+ -> copper (I) (need 2 to bond with oxygen)
Cu2+ -> copper (II) (need one to bond with oxygen)
Explain dot and cross diagrams for ionic bonds
Positive and negative ions are attracted to each other -> electrostatic attraction -> ionic bond
Makes lattice -> stable
Ex:
Sodium has one electron on outer shell (cation -> cross)
Chlorine has 7 electrons on outer shell (anions -> dots)
Sodium (cation) gives one electron to chlorine (anions) -> cross goes to empty spot on chloride
Becomes NaCl (neutral compound)
What the ‘formula’ for ionic compounds?
Symbol with charge for both
Balance the charge -> criss cross method (always simplify)
Always cation then anion
Name -> cation anion+ide
What are some compound ions?
Hydroxide -> OH-
Sulphate -> SO 2- (subscript 4)
Nitrate -> NO- (subscript 3)
Carbonate -> CO 2- (subscript 3)
Ammonium -> NH+ (subscript 4)
Hydrogen-carbonate -> HCO- (subscript 3)
WHEN USING COMPOUND IONS IN IONIC COMPOUNDS USE BRACKETS
Describe the characteristics of ionic compounds
Compounds are pack in alternating pos and neg ions
Form crystals (+lattice when solid)
Very strong bond (lots of heat too break)
Solid at room temp
High melting and boiling point
Don’t conduct electricity
- can when molten (lattice broken electrons/ions free to move)
Soluble in water
- can carry current when dissolved
Brittle (bc of structure)
What elements are bonded by covalent bonding?
Non-metals form simple molecules by covalent bonding
Draw diagrams of covalent bonding using dot and cross diagrams
Ex: 2 hydrogen
One hydrogen-cross
Second hydrogen-dot
Overlap (intersection of the venn diagram) -> one dot one cross
-> both need 2 to be stable, they share electrons and become stable
H-H
Look on revision guide for others if necessary
Use dot and cross diagrams to show more complex covalent molecules
Carbon dioxide ->C=O=C
Between carbon and oxygen there are 2 pairs of covalent bonds
How do you name and write covalent bonds?
Formula
Element with subscript of amount of atoms
Name
Elements in name of formula
Prefix (unless mono for first)
Element1 element2-ide
What are the differences in volatility, solubility and electrical conductivity between the two different types of bonding?
Ionic compounds
Non-volatile
High melting and boiling point
Usually soluble in water but not in organic solvents
Conduct electricity under molten or aqueous states
Covalent compounds
Volatile
Low melting and boiling points
Insoluble in water but soluble in organic solvents
Cannot conduct electricity solid or liquid states
Why are the difference is melting and boiling points between the two types of bonds a result of attractive forces?
Molecules (covalent) -> weaker intermolecular forces -> less energy required to break the bond
Molecules (ionic) -> stronger intermolecular forces -> more energy required to break bonds
What are different structure of the same element called?
Allotroped -> diamonds and graphite are chemically identical but have different physical properties
Describe the giant covalent structure of graphite and diamond
Graphite -> soft and slippery
Can conduct electricity
Layered with weak bonds-> used to write
Diamonds -> tetrahedral structure
Multiple strong bonds
Insulator
Describe the macromolecule structure of silicon (IV) oxide (silicon dioxide (SiO2))
Silicon dioxide (quartz) is giant covalent structure with a tetrahedral structure similar to that of a diamond
Why is balancing equations important?
In chemical reactions you never lose particles, so what was there at the beginning must be there in the end (even if a different form)
Define relative atomic mass (A)
Average mass of naturally occurring atoms of an element on a scale, taking all isotopes into account
Percentage x mass
Define relative molecular mass
Sum of the relative atomic masses
Ex: H20
H=1 O=16
1x2 + 16= 18
What is a mole?
A mole of an element contains the same amount of elementary units as 12g of Carbon 12
What is Avogardo’s number?
The number of particles in a mole
6.022 x 10^23 particles/mole
What is the mass of a mole called?
Molar mass (MM)
-g/mol (grams/mole)
What is the molar volume of any gas at a standard temp and pressure? How much is 1 dm^3 in liters?
24 dm^3 -> volume
24 dm^3/mol -> molar volume
1 dm^3 -> 1L
What is the equation for the number of moles (volume)?
Number of moles=volume/molar volume
How are concentrations of a solution measured?
-g/dm^3
-mol/dm^3
How can you get the chemical formula using the total mass of the separate elements?
- Find the molar mass /// or number of moles
- Find the simplest ratio
How can you find the number of moles (mass)?
Number of moles = mass/MM
How can you calculate the mass of a product of a chemical reaction by knowing the mass of the starting elements?
Ex:
CaO + CO2= CaCO2
56 + 44= 100
CaCO2 = 100g
What is the mass of aluminum oxide if 9.2g of aluminum reacts with oxygen?
- Convert 9.2g to moles (9.2/27 -> 0.34 moles)
- Take the ratio from the equation (4:2) and apply to the amount of mole (0.34:0.17)
- Use mole=mass/MM to find the mass of the aluminum dioxide (17.3g)
What is the equation for the amount of mole (involving concentration)?
Number of moles=concentration/1000 x V (in cm^3)
REMEMBER: 1dm^3 = 1000 cm^3
What is titration?
Using the known concentration of one solution to figure out the unknown concentration of another solution
Hydrochloric acid is titrated against standard sodium hydroxide solution
20cm^3 of acid neutralises 25cm^3 of 0.10mol/dm^3 of sodium hydroxide solution
Find the concentration of the hydrochloric acid solution
- Number of moles (NaOH)
0.10/1000 x 25 = 2.5 x 10^-3 - Number of moles (acid)
HCl + NaOH -> NaCl + H2O
One mole of HCl neutralizes one mole NaOH
So, 2.5 x 10^-3 mol of NaOH neutralizes 2.5 x 10^-3 mol of HCl - Titration value
2.5 x 10^-3 = concentration/1000 x 20 =0.125 mol/dm^3
Describe the characteristics of covalent bonds
Structure
Bonds
At room temp
Melting point
Conductivity
Forms molecules
Weaker bonds
Liquid or gas at room temp
Low melting point
Don’t conduct electricity
