chem š§Ŗāļø Flashcards
practice questions and notes
what are the states of matter
solids liquids and gases
what is particle theory?
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.
what are the different stages of changes in matter?
melting, boiling (evaporating), condensing and freezing.
how are solids, liquids and gases different?
slg have different properties depending on how strongly particles are held together.
solids vs liquids vs gases
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.
why do s l g behave differently?
In substances, particles are constantly in motion. However, these movements differ according to the state of matter and according to the energy levels.
energy according to s l g
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
how do substances change from one state to another?
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.
explain what happens during evaporation
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.
what are some examples of unusual cases where substances dont follow the laws of particle theory?
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 āinfinite fluidityā and will āclimb outā 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.
what are elements
They are substances that cant be broken down into anything simpler because they are made of only one type of the same atom.
What are molecules
Two or more atoms chemically bonded.
Both elements and compounds can be considered molecules.
what are compounds
A substance made up of two or more types of atoms (elements)
what are mixtures
a material made up of two or more different chemical substances which are NOT chemically bonded.
what is diffusion
the random mixing and moving of particles in liquids and gases (generally from a region of higher concentration to a region of lower concentration)
in which three states of matter are the particles moving the fastest
gases.
what is paper chromatography?
a way of separating or identifying solutions or liquids that are mixed together.
how can substances be identified through chromatography?
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
whats a simple way of checking the purity of solids and liquids?
using heat to find the temperature at which it boils or melts.
an impure solid will have a _____ melting point than a pure solid
lower
a liquid containing a dissolved solute will have a ______ boiling point than the pure solvent.
higher
methods of purification
filtration, evaporation, filtration+evaporation, distillation, fractional distillation.
(refer to notebook to study the methods)
what are factors of chemical changes?
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.
in chemical changes, can mass technically change?
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.
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
what can most elements be classified as?
metal or non metal
in a periodic table, how are metals arranged?
metals are on the left and middle, non metals are on the right.
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
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.
how is an alloy formed
when metals are mixed with other elements.
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.
what are the three main subatomic particles?
protons, electrons and neutrons.
how can the masses of subatomic particles be measured
using the relative scale. Their charges may also be compared in a similar way.
the proton and neutrons have the ______ mass and protons and electrons have ________but opposite charges
same, equal
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.
what is the mass of the electron in comparison to protons and neutrons?
1/2000 of the masses of p and n
what unit do scientists use to measure the number protons?
atomic number.
what unit do scientists use to measure the number of particles in the nucleus?
nucleon number.
what is atomic unit used for?
it is used to arrange the elements in the periodic table.
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
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
how are electrons arranged in the structure of an atom?
they are arranged in shells around the nucleus.
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.
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
what are the electrons in the outer shells that are involved in chemical bonding known as?
valency electrons.
what is the electron arrangement in an atom called?
electric configuration.