States of Matter + Atoms Elements and Compounds

Solids

• Solids have a fixed volume and shape and they have a high density.

• The atoms vibrate in position but can’t change location

• The particles are packed very closely together in a fixed and regular pattern

Liquids

• Liquids also have a fixed volume but adopt the shape of the container

• They are generally less dense than solids (an exception is water), but much denser than gases

• The particles move and slide past each other which is why liquids adopt the shape of the container and also why they are able to flow freely

Gases 

• Gases do not have a fixed volume, and, like liquids, take up the shape of the container

• Gases have a very low density

• Since there is a lot of space between the particles, gases can be compressed into a much smaller volume

• The particles are far apart and move randomly and quickly (around 500 m/s) in all directions

• They collide with each other and with the sides of the container

How is pressure inside a can created

Particles collide with each other and with the sides of a container

solid to liquid

melting

liquid to solid

freezing

liquid to gas

evaporation, boiling or vaporization

gas to liquid

condensation

solid to gas

sublimation

gas to solid

desublimation or deposition

Melting

• when a solid changes into a liquid

• Requires heat energy which transforms into kinetic energy, allowing the particles to move

• Occurs at a specific temperature known as the melting point (m.p.) 

Freezing

• when a liquid changes into a solid

• This is the reverse of melting and occurs at exactly the same temperature as melting, hence the melting point and freezing point of a pure substance are the same. Water, for example, freezes and melts at 0 ºC

• Requires a significant decrease in temperature (or loss of thermal energy) and occurs at a specific temperature 

Boiling

• when a liquid changes into a gas

• Requires heat which causes bubbles of gas to form below the surface of a liquid, allowing for liquid particles to escape from the surface and within the liquid

• Occurs at a specific temperature known as the boiling point (b.p.)

Evaporation

• occurs when a liquid changes into a gas and occurs over a range of temperatures

• Evaporation occurs only at the surface of liquids where high energy particles can escape from the liquid's surface at low temperatures, below the b.p. of the liquid

• The larger the surface area and the warmer the liquid surface, the more quickly a liquid can evaporate

Condensation

• Condensation occurs when a gas changes into a liquid on cooling and it takes place over a range of temperatures

• When a gas is cooled its particles lose energy and when they bump into each other they lack the energy to bounce away again, instead they group together to form a liquid

When substances are heated,

the particles absorb thermal energy which is converted into kinetic energy

basis of the kinetic theory of matter

When substances are heated, the particles absorb thermal energy which is converted into kinetic energy

Describe how a solid turns into a liquid

Heating a solid causes its particles to vibrate more

As the temperature increases, the particles vibrate so much that the solid expands until the structure breaks

Describe how a liquid turns into a gas through evaporation

• Heating a liquid causes its particles to move more and spread out

  • Some particles at the surface gain sufficient energy to overcome the intermolecular forces

  • This is when a liquid starts to evaporate

Describe how a liquid turns into a gas through boiling

• Heating a liquid causes its particles to move more and spread out

• When the boiling point is reached, all of the particles gain enough energy to escape and the liquids boils into a gas

Heating and cooling curves are used to

• show how changes in temperature affect changes of state

During a state change

there is no temperature chance

During a phase change, a substance's temperature remains constant because

the energy involved is used to break bonds and change the state of matter, rather than increasing the kinetic energy of the substance's molecules. This process is called latent heat. 

latent heat

the heat needed to cause a phase change to a specific amount of matter at a fixed temperature

A change in temperature or pressure affects the

volume of gases

As the air inside a hot air balloon is heated up

it expands and the balloon gets bigger. This is because the volume of a gas increases as temperature increases

the volume of a gas increases

as temperature increases. The density decreases as the volume increases so the balloon rises.

If you have a gas stored inside a container that is squeezed, the pressure

increases as you decrease the volume

Gaseous particles are

in constant and random motion

The pressure that a gas creates inside a closed container is produced by

the gaseous particles hitting the inside walls of the container:

How does temperature affect the volume of a gas?

Increasing the temperature increases the kinetic energy of each particle. As the temperature increases, the particles in the gas move faster and spread out more. If the gas particles are inside a container, they will collide with the container walls more frequently. If the container walls are flexible and stretchy then the container will get bigger and bigger, just like the hot air balloon!

How does pressure affect the volume of a gas?

Pressure is about the number of particles in a given volume. Increasing the pressure means that there are the same number of particles but in a smaller volume. Conversely, decreasing the pressure means that there are the same number of particles but in a larger volume

When the pressure increases

the volume decreases. This means that the molecules collide with the container walls more frequently

Diffusion occurs in

gases and liquids, due to the random motion of their particles

Why does diffusion occur

because of the random motion of their particles

Diffusion

where particles move from an area of high concentration to an area of low concentration. Eventually the concentration of particles is even as the particles are evenly spread throughout the available space

Diffusion happens on

its own and no energy input is required

Diffusion occurs faster at

higher temperatures because the particles have more kinetic energy

Diffusion is faster in gases than

liquids

Why is diffusion faster in gases than in liquids?

because gaseous particles have more energy and move quicker than liquid particles

the diffusion of bromine gas and air

At the start, the orange-brown bromine gas is an area of high concentration

It diffuses from a high to low concentration

After 5 minutes, the bromine gas will have diffused from the bottom jar until it is evenly spread throughout both jars

The same can be said for the air, although it is less obvious as it is colourless

How molecular mass affects diffusion

At the same temperature, different gases do not diffuse at the same rate.

This is due to the difference in their relative molecular masses

Gases with a lower relative molecular mass are "lighter" which means that they Travel faster, travel further in the same amount of time

The reverse argument is true for gases with a high relative molecular mass, they Travel slower and Do not travel as far in the same amount of time

Diffusion of ammonia and hydrogen chloride

Ammonia gas and hydrogen chloride gas react together to form solid ammonium chloride. Ammonia molecules have less mass than HCl molecules so they diffuse faster and the product forms closer to the HCl end

Four substances are shown, in which of these substances are the particles closer together and moving slowly past eachother?

A) Ice

B) Air

C) Steam

D) Water

D) Water

A student noted the following observation in his book: The particles moved slowly from an area of high concentration to an area of low concentration.
Which process is being described?
A) Diffusion of a substance in a liquid

B) The particles of a solid when melting

C) A liquid being frozen

D) DIffusion of a substance through the air

A) Diffusion of a substance in a liquid

A small amount of bleach was accidentally spilled on the kitchen floor. After a while it was observed that the floor appeared to be dry and the room smelled of bleach. What processes have occured?
A) Evaporation and diffusion

B) Distillation and diffusion

C) Evaporation only

D) Diffusion only

A) Evaporation and diffusion

Characteristics of silicon (IV) oxide

very high melting point and boiling point and does not conduct in any form

Room temperature

between 20 to 25 degrees celsius

To be a metal

A substance must be a good conductor in all states and it must have a relatively high melting point

Aqueous sodium chloride

conducts as a liquid solution but not as a solid. The boiling point of water is elevated by the presence of sodium chloride and the melting point is depressed

an ionic compound conducts when

liquid but not solid, the melting and boiling point should also be high

chemical equation for the reaction of ammonia and hydrogen chloride

NH3 + HCl —> NH4Cl

Name the process by which ammonia and hydrogen chloride gases move in the tube

diffusion

What would be the result of an impure substance in a heating or cooling curve?

Lines would not be horizontal and the line would be lower

All substances can be classified into one of these three types

• Elements

• Compounds

• Mixtures

What is an element?

a pure substance that cannot be broken down into any other substance. Every element is made up of its own type of atom. Made of atoms that all contain the same number of protons.

What is a compound?

A pure substance made up of two or more elements chemically combined

What is a mixture?

A combination of two or more substances (elements and/or compounds) that are not chemically combined

How can mixtures be seperated?

by physical methods such as filtration or evaporation

All substances are made of tiny particles of matter called 

atoms which are the building blocks of all matter

Each atom is made of subatomic particles called 

protons, neutrons, and electrons

Location of subatomic particles in an atom

nucleus - protons and neutrons
outer shells - electrons

proton mass and charge

mass - 1

charge - +1

neutron mass and charge

mass - 1

charge - 0

electron mass and charge

mass - 1/1840

charge - -1

atomic number (or proton number)

The number of protons in the nucleus of an atom

symbol for atomic number

Z

You can find out the number of electrons in an atom

by looking at the atomic number as the number of protons and electrons are the same

Nucleon number (or mass number)

the total number of protons and neutrons in the nucleus of an atom

symbol for nucleon number

A

The nucleon number minus the proton number gives you

the number of neutrons of an atom

protons and neutrons can collectively be called

nucleons

the mass number is always greater than the

atomic/proton number

We can represent the structure of the atom in two ways:

using diagrams called electron shell diagrams or by writing out a special notation called the electronic configuration

Electron shell diagrams

Electrons orbit the nucleus in shells (or energy levels) and each shell has a different amount of energy associated with it. The first shell can hold 2 electrons, the rest, up to 8.

The outermost shell of an atom is called

the valence shell and an atom is much more stable if it can manage to completely fill this shell with electrons 

What is the electronic configuration of boron?

2, 3

electronic configuration of oxygen

2, 6

electronic configuration of calcium

2, 8, 8, 2

How does the electronic structure of an element relate to its location in the Periodic Table?

The number of notations in the electronic configuration will show the number of occupied shells of electrons the atom has, showing the period in which that element is in. The last notation shows the number of outer electrons the atom has, showing the group that element is in (for elements in Groups I to VII).

Rows in the periodic table are called

periods

horizontal lines in the periodic table are called

groups

how to know which period an element is in

The number of notations in the electronic configuration will show the number of occupied shells of electrons the atom has

how to know which group an element is in

The last notation shows the number of outer electrons the atom has

Period: The red numbers at the bottom show the number of notations

The number of notations is 3

Therefore the element has 3 occupied shells 

Group: The last notation, in this case 7

This means that the element has 7 electrons in its outer shell

Element is therefore in Group 7

The noble gases

in group 8 or 0

All of the noble gases are unreactive as they have full outer shells and are thus very stable

Atoms want their shells to be

full

Why do atoms want their shells to be full?

It makes them more stable, in some cases atoms lose electrons to empty its shell so that the next shell below is full. Then they’d have the electronic structure of a noble gas.

electrons in the outer shell are also known as

valency electrons. 

isotopes

Isotopes are different atoms of the same element that contain the same number of protons but a different number of neutrons. This means that the mass number would change while the proton number would stay constant.

Why do isotopes share properties or same chemical characteristics

because they have the same number of electrons in their outer shells, and this is what determines their chemistry

The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only

The difference in mass affects the physical properties, such as density, boiling point and melting point

What does the difference in mass affect in isotopes?

physical properties like density, boiling point and melting point because of the added mass from neutrons

Relative atomic mass

Atoms are so tiny that we cannot really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass (A_r) is used

The relative atomic mass unit is equal to

1/12th the mass of a carbon-12 atom

Why does relative atomic mass have no units?

All other elements are measured by comparison to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units

relative atomic mass formula

(% of isotope A x mass of isotope A) + (% of isotope B x mass of isotope B)

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100

do this question

85.6

Is mass number and relative atomic mass the same thing?

No. mass number is the sum of protons and neutrons present in the nucleus of an atom and it is a whole number value while relative atomic mass is the ratio of the mass of an element to the 1/12th of the mass of a carbon atom.

What is an ion?

an electrically charged atom or group of atoms formed by the loss or gain of electrons