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🔥Gcse studies🔥 (personal) > chem 🧪⚗️ > Flashcards

chem 🧪⚗️ Flashcards

practice questions and notes

1
Q

what are the states of matter

A

solids liquids and gases

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2
Q

what is particle theory?

A

It is based on the idea that all substances are made up of extremely tiny particles.

The particles in the three different states of matter are arranged differently and have different types of movement and different energies.

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3
Q

what are the different stages of changes in matter?

A

melting, boiling (evaporating), condensing and freezing.

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4
Q

how are solids, liquids and gases different?

A

slg have different properties depending on how strongly particles are held together.

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5
Q

solids vs liquids vs gases

A

solids: they have a fixed volume and shape.

liquids: have a fixed volume but not a definite shape. They take up the shape of the container.

gases: have no fixed volume or shape. Particles spread out in order to fill any container or space.

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6
Q

why do s l g behave differently?

A

In substances, particles are constantly in motion. However, these movements differ according to the state of matter and according to the energy levels.

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7
Q

energy according to s l g

A

solids: particles are held tightly together and although they rent free to move around, they vibrate on the spot because they still have some energy.

liquids: In liquids, particles are held tightly together, however they have more energy than solids which make them move around.

gases: In gases, particles are loose and have enough energy to move around and apart from eachother, constantly moving. Gas particles spread apart to keep moving

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8
Q

how do substances change from one state to another?

A

solid->liquid->gas
This transition the addition of heat energy which is given to cells to break apart imf (inter molecular force) as the cells themselves move apart from eachother.

gas->liquid->solid
this requires the removal of heat energy. Particles move closer together and bond as liquid->solid.

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9
Q

explain what happens during evaporation

A

the particles in liquid have different energy levels so some are moving faster than others. Those particles which move faster escape from the surface causing evaporation.

The rate of evaporation increases as external temperatures increase.

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10
Q

what are some examples of unusual cases where substances dont follow the laws of particle theory?

A

superfluids: when liquids are cooled down to very low temperatures, they develop into a second liquid state called superfluid. Liquid helium at just above zero has “infinite fluidity” and will “climb out” of its container when left undisturbed.
plasma

plasma: can exist at temperatures of several thousands of degrees. An example of plasma is charged air produced by lightening. Like gas, a plasma does not have a definite shape or volume but its strong forces between particles give it strange properties such as electrical conductivity.

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11
Q

what are elements

A

They are substances that cant be broken down into anything simpler because they are made of only one type of the same atom.

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12
Q

What are molecules

A

Two or more atoms chemically bonded.

Both elements and compounds can be considered molecules.

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13
Q

what are compounds

A

A substance made up of two or more types of atoms (elements)

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14
Q

what are mixtures

A

a material made up of two or more different chemical substances which are NOT chemically bonded.

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15
Q

what is diffusion

A

the random mixing and moving of particles in liquids and gases (generally from a region of higher concentration to a region of lower concentration)

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16
Q

in which three states of matter are the particles moving the fastest

A

gases.

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17
Q

what is paper chromatography?

A

a way of separating or identifying solutions or liquids that are mixed together.

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18
Q

how can substances be identified through chromatography?

A

by calculating retention factor; this is the distance a substance has travelled up the filtered paper/ the distance travelled by the solvent.

As the solvent will always travel further, Rf will always be >1

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19
Q

whats a simple way of checking the purity of solids and liquids?

A

using heat to find the temperature at which it boils or melts.

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20
Q

an impure solid will have a _____ melting point than a pure solid

A

lower

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21
Q

a liquid containing a dissolved solute will have a ______ boiling point than the pure solvent.

A

higher

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22
Q

methods of purification

A

filtration, evaporation, filtration+evaporation, distillation, fractional distillation.

(refer to notebook to study the methods)

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23
Q

what are factors of chemical changes?

A

in a chemical change, one or more substances are produced.

In many cases, an observable change is apparent; for example, change in colour or formation of gas.

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24
Q

in chemical changes, can mass technically change?

A

no; according to the law of conservation of mass, mass cannot be created or destroyed

. Therefore if a change in mass is seen in a reaction, this would be due to the formation of gas which might have escaped.

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25
in chemical changes, what kind of change is involved most of the time?
energy change; energy is either released or gained and absorbed (exothermic, endothermic) Some physical changes also undergo energy changes; for example water s->l->g vise versa
26
what can most elements be classified as?
metal or non metal
27
in a periodic table, how are metals arranged?
metals are on the left and middle, non metals are on the right.
28
physical and chemical properties of metals
-Ductile; can be draw into a wire -Good conductors of heat -Good conductors of electricity -high melting points -shiny -malleable; can be hammered into a shape -sonorous; rings when struck *anomalies: -the alkali metals have a low melting point. -Mercury has a low melting point
29
physical and chemical properties of non metals
-brittle -poor conductors of electricities -poor conductors of heat -dull -low melting points *anomalies: -carbon in the form of graphite is a good conductor of electricity -carbon and silicon have high melting points.
30
how is an alloy formed
when metals are mixed with other elements.
31
whats an example of a chemical reaction that can be reversed?
when hydrated blue copper sulfate crystals are heated, a white powder is formed and water is lost as a stream. If water is added to this white powder, hydrated blue copper sulfate is formed again.
32
what are the three main subatomic particles?
protons, electrons and neutrons.
33
how can the masses of subatomic particles be measured
using the relative scale. Their charges may also be compared in a similar way.
34
the proton and neutrons have the ______ mass and protons and electrons have ________but opposite charges
same, equal
35
where are protons, neutrons and electrons found in an atom?
protons and neutrons are found in the center of the atom in a cluster called the nucleus. The electrons form a series of shells around the nucleus.
36
what is the mass of the electron in comparison to protons and neutrons?
1/2000 of the masses of p and n
37
what unit do scientists use to measure the number protons?
atomic number.
38
what unit do scientists use to measure the number of particles in the nucleus?
nucleon number.
39
what is atomic unit used for?
it is used to arrange the elements in the periodic table.
40
what are isotopes?
Isotopes are atoms with the sane number of protons and electrons but different numbers of neutrons. e.g Carbon 14 is an isotope of carbon, with 8 neutrons and 6 neutrons
41
do the chemical properties of isotopes differ from the original atom?
no, as the chemical properties of atoms depend on the arrangement of electrons in their atoms
42
how are electrons arranged in the structure of an atom?
they are arranged in shells around the nucleus.
43
how many electrons can the shell nearest to the nucleus hold?
max. 2. The next one out from the nucleus can take up from 8.
44
if in an oxygen atom, there are two electrons in the first shell and six are in the next shell, whats the arrangement
2,6
45
what are the electrons in the outer shells that are involved in chemical bonding known as?
valency electrons.
46
what is the electron arrangement in an atom called?
electric configuration.
47
what increases, moving through a section or period of the periodic table? and what is this called
the electron number increases. This is called periodicity.
48
elements that have similar electron configurations have ______
similar chemical properties e.g lithium, sodium, potassium all have one electron in their outer shells. They are also group 1 elements which are highly reactive metals.
49
why are helium, neon, argon and krypton so unreactive?
they all have 8 electrons in their outer shells or full outer shells this means the atoms don't lose or gain electrons easily.
50
what is formed when one of the reacting atoms is a metal and the other is a non metal?
an ionic compound. it is made up of ions.
51
ionic compounds have similar _______ and are quite different from the properties of substance made up of ______ and _______
physical properties atoms molecules
52
how are ions formed?
through the gain and loss of electrons. Both metals and non metals try to achieve complete (filled) outer electron shells.
53
when metals lose elctrons from their outer shells what is formed?
positive ions.
54
what is formed when non-metals gain electrons in the outer shells?
negative ions.
55
whats an example of ionic bonding?
sodium has 11 electrons arranged 2,8,1. chlorine is a non metal and has 17 electrons, arranged 2,8,7. The sodium atom can achieve a full outer shell by losing an electron. The chlorine atom can achieve a full outer shell by gaining an electron. The sodium atom transfers the electron. The sodium atom is no longer an atom, its an ion. The chlorine is also not an atom, its an ion. They are both no longer neutral. The sodium atom has one less electron than the number of protons. It has a positive charge. Its written as NA^+ (u dont write the 1 but when its 1< u write) the chlorine atom has 1 more electron than the total number of protons and becomes a negative ion.
56
can metals transfer more than one electron to a non metal?
yes. e.g magnesium combines with oxygen to form magnesium oxide. The magnesium (2,8,2) transfers two electrons to the oxygen atom (2,6) Magnesium thus forms Mg+2 ion and oxygen forms O-2
57
oxidation vs reduction
when in the process of forming an ionic compound, the atom that loses electrons is said to be oxidised. the atom that gains electrons in reduced.
58
when atoms form ions, they are trying to achieve the electronic configuration of their nearest ________
noble gas - due to their stable electronic configuration (eight electrons in outer shell)
59
properties of ionic compounds
-high melting point and boiling point- due to strong electrostatic forces (ionic bond) - form giant lattice structures e.g sodium chloride is formed by ionic bonding but the ions, rather than pairing up, each sodium ion is surrounded by six chloride ions and vice versa
60
What are some examples of ionic compounds
sodium chloride (salt), magnesium oxide
61
why does an ionic compound like magnesium oxide or sodium chloride not conduct electricity when it is solid?
Due to the strong ionic bonds, the ions are prevented from moving.
62
why does sodium chloride dissolve in water
the water is also able to form strong electrostatic attractions with the ions. The ions are 'plucked' off the lattice structure.
63
why does sodium chloride conduct electricity when molten or dissolved in water?
The strong forces between the ions have been broken down and so the ions are able to move.
64
what are ions
Ions are atoms or molecules that have gained or lost one or more electrons, resulting in a net electric charge.
65
what is the relationship between number of protons, neutrons and electrons?
- in a neutral atom, number of protons=number of electrons -the number of neutrons do not have to equal number of protons.
66
What are covalent bonds?
Covalent substances are formed when atoms of non-metals combine. Although covalent substances all contain the same type of bonds, their properties can be quite different.
67
How are covalent bonds formed?
Covalent bonding occurs through electron sharing between atoms of non-metals. This results in the formation of a molecule.
68
Why are covalent bonds formed
Because the non-metal atoms try to achieve complete outer electron shells or the electron arrangement of the nearest noble gas by sharing electrons.
69
How is a single covalent bond formed
when two atoms each contribute one electron to a shared pair of electrons. A single covalent bond can be represented by a single line. e.g hydrogen gas exists as. H2 molecules. Each hydrogen atom needs to fill its electron shell. They can do this by sharing electrons.
70
How does the attraction work in covalent bonding?
The bonding pair of electrons are negatively charged and the nuclei is positively charged.
71
Key difference between Ioninc bonding and Covalent bonding
Ionic bonding is when electrons are TRANSFERRED from one atom to another. Covalent bonding is when electrons are SHARED between atoms of the opposite charge.
72
What are example of molecules that contain double covalent bonds
-Carbon dioxide The atom has an arrangement of 2,4 and needs and additional four electrons to complete its outer electron cell. 4 electrons from oxygen atoms. -C2H4 (ethene)
73
What are examples of molecules that contain triple covalent bonds
in a nitrogen molecule each nitrogen atom has an electron arrangement of 2,5 and needs an additional three electrons to complete its outer shell. It need to share three of its outer electrons with another nitrogen atom. This forms a triple bond.
74
How many covalent bonds can an element form?
This is linked to the element's position in the periodic table. Group in periodic table: no. covalent bonds: 1 0 2 0 3 0 4 4 5 3 6 2 7 1 8 0
75
What can covalent compounds form?
simple molecular crystals.
76
What form do many covalent crystals exist in?
solid forms at low temps
77
examples of molecular crystals
ice, solid CO2, iodine
78
Covalent bonds are _____, ______ bonds formed within each molecule
strong, intermolecular
79
What usually are substances with molecular structures
gases, liquids or solids with low melting points and boiling points.
80
Explain the properties of covalent compounds using the properties of hydrogen.
Hydrogen is a gas with a very low melting point (-259C)- The intermolecular forces of attraction between the molecules are week Hydrogen does not conduct electricity- There are no ions or free electrons present, The covalent bond is a strong bond. For a substance to conduct electricity, there needs to be free- moving charge carriers
81
What are the bonds between molecules like?
the intermolecular forces of attraction are weak.
82
Compare the properties of covalent and ionic compounds
Volatility (How easily it forms vapour): Ionic compounds- Non-volatile high melting and boiling points Covalent compounds- Volatile (low melting and boiling points) Solubility Ionic compounds- Often soluble in water Covalent compounds- Mostly insoluble on water Electricity conductivity: Ionic compounds- Conducts electricity only when dissolved in water or molten (the ions are free to move, carrying the electric charge) Covalent compounds-Low electrical conductivity- are non-electrolytes, do not contain ions and thus cant carry electric current. Intermolecular force Ionic: strong Covalent: weak
83
What structure is a diamond?
Tetrahedral lattice
84
What are different forms of the same element e.g (diamond, graphite (carbon))
allotropes
85
How many covalent bonds does each carbon atom form in a diamond
four
86
How many covalent bonds does each carbon atom form in a graphite
three
87
What are the forces of attractions between the layers in graphite like
weak
88
What causes diamond and graphite to have high sublimation and melting points?
Because they are held together by very strong bonds.
89
How is the make up of graphite different from diamonds
Carbon atoms form layes or hexagons in the plane of the strong covalent bonds. the weak forces are between the layers. Layers can slide over eachother so graphite can be a lubricant.
90
Why can graphite conduct electricity
Because the fourth unbonded electron from each carbon atom is delocalised and thus can move along the layer.
91
How can structures be identified
as giant or molecular
92
How do you differentiate 'giant' and 'molecular' structures?
with their melting points
93
What is stoichiometry
The area of chemistry concerned with the relative quantity of reactants and and products in a chemical reaction
94
What can a compound be represented by
a chemical formula
95
what does the 'combining power' refer to
The term combining power usually refers to valency, which is the ability of an atom to combine with other atoms. Valency is based on the number of electrons an atom can gain, lose, or share when it forms chemical bonds.
96
For periodic groups 1-4 what determines the 'combining power'
its group number e.g sodium is in group 1- its 'combining power' (valency) is 1
97
For periodic groups 5-7 what determines the 'combining power'
8-(its group number) chlorine is in group 7- its valency is 1
98
What determines 'combining power' if the element is not in one of the main groups
It's included in the name of the compound containing it e.g iron(II) oxide iron has valency of 2
99
In what other cases is the 'combining power' included in the compound
if the valency is not what you expect it to normally be e.g phosphorus is in group V so it should have valency of 3 but in Phosphorus (V) oxide, it has a valency of 5
100
Why is hydrogen different in terms of valency
It does not belong to a group, and its valency is not stated in the compound. Its valency is 1.
101
How do you work out the chemical formula of magnesium oxide (give me a step by step)
1. write down the name of the compound -Magnesium oxide 2. write down the chemical symbols for the elements -Mg O 3. use the periodic table to find out the 'combining power' of each element under its symbol -Mg is in group 2- valency=2 -Oxygen's valency is 2 4. If the numbers can be cancelled down do so. -Mg-1 O-1 *If they have the same valency, you cancel the numbers out* 5. (doesnt apply to this case) Swap the combining powers, write them after the symbol slightly below the line (subscript) MgO
102
Work out the formula for calcium chloride
Cu Cl 2 1 valency=2 valency= 1 *swap* CuCl₂
103
what is a radical
A radical is a species (atom, molecule, or ion) that has one or more unpaired electrons, making it highly reactive.
104
What radicals have valency of 1
-Hydroxide (OH) -Hydrogencarbonate (HCO₃) -nitrate(NO₃) -Ammonium(NH₄)
105
What do valency do these have -Hydroxide -Hydrogencarbonate -nitrate -Ammonium
1
106
what radicals have valency of 2
-carbonate (CO₃) -sulfate (SO₄)
107
What valency do these have -carbonate -sulfate
2
108
What radical has a valency of 3
Phosphate (PO₄)
109
When does a radical have to be put in brackets Give an example
When the formula contains more than one radical unit e.g Calcium (Ca) Hydroxide (OH) 2 1 *swap* Ca(OH)₂
110
What valency does Phosphate (PO₄) have
3
111
Whats the difference between CaOH₂ and Ca(OH)₂
In CaOH₂ -> one Ca, one O, two H In Ca(OH)₂-> one Ca, two O, two H
112
Calculate the formula for sodium chloride (an ionic compound)
-Sodium (Na) is in group 1 and forms an ion with a charge of +1 -Chlorine (Cl) is in group 7 and forms an ion with a charge of -1 When these ions combine, their charges cancel eachother out: NaCl
113
Calculate the formula for Lead Bromide (an ionic compound)
Lead- Pb (+2) Bromide- Br (-1) To cancel out the charge +2 from the lead 2 bromide molecules are needed to make -2: PbBr₂
114
Diatomic elements
H₂- Hydrogen (Have) N₂- Nitrogen (No) F₂- Fluorine (Fear) O₂- Oxygen (Of) I₂- Iodine (Ice) Cl₂- Chlorine (Cold) Br₂- Bromine (Beer)
115
Hydrogen burns with a 'pop' when reacted with oxygen in the air to form water. Write and balance a chemical equation to describe this
H₂+O₂->H₂O 2H₂+O₂->2H₂O 4 H's 4 H's 2 O's 2 O's
116
Balance and write this in a balanced chemical equation Lead(II) nitrate + Potassium iodide -> Lead(II) iodide + Potassium nitrate Pb(NO₃)₂ + KI -> PbI₂ + KNO₃
Pb(NO₃)₂ + 2KI -> PbI₂ + 2KNO₃
117
Ethane burns in air to form carbon dioxide and water. Balance this chemical equation for it: C₂H₆ + O₂ -> CO₂ + H₂O
2C₂H₆ + 7O₂ -> 4CO₂ + 6H₂O

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