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Substances exist in one of four phases: gas, liquid, solid, and plasma.
Substances change between the phases depending on their temperature. Boiling, melting, condensing, and freezing are all processes that change a substance’s state.
Molecules connect together to form all kinds of substances. Depending on the properties of the matter and what temperature it is, substances can be in one of four states, or phases: gas, liquid, solid, and plasma.
In a gas, there is a lot of space between the molecules. Liquids have less space between molecules and can change shape. Both gases and liquids are fluids, which means they can change shape according to where they are. Solids have very little space in between the molecules. They cannot flow (move like fluid) and they have a more fixed shape.
Plasma is a hot gas with different properties. It is considered a fourth phase of matter, but we do not interact with it as often as the other three phases.
Look at the example of water. At room temperature, water is a liquid. If you heat water up, it becomes a gas (steam). And if you make it cold enough, it freezes and becomes a solid (ice).
Figure 12.3: This picture shows water in all three phases.
This picture shows water in all three phases.
Substances melt from solid to liquid and boil from liquid to gas. The changes can go in the other direction too. Condensing is what happens when a gas changes to a liquid. Freezing is the process that changes a liquid into a solid (like freezing water into ice). Different substances change their state at different temperatures, depending on what they are made of. Water freezes at 32 degrees Fehrenheit (0 degrees Celcius) but other substances might freeze at different temperatures.
Atomic mass
The atomic mass of an atom is the number of protons plus the number of neutrons that it contains.
The mass of an atom stays the same even when its state changes.
In science, especially chemistry and physics, the word mass has a very specific meaning. Mass is a property of matter and does not change.
The atomic mass of an atom is the number of protons plus the number of neutrons that it contains. (Some of the numbers are partial numbers, or decimals. That’s because the numbers of neutrons in an atom can vary, so the atomic mass number is an average). The mass of any one atom is the same no matter what the temperature is, what state it is in, or whether or not the atom is part of a molecule.
People often confuse mass with weight, which is how heavy something is. This is mostly because in English we often use the word weight when we actually mean mass, and the other way around. Weight can change because it depends on gravity (you will cover gravity in your physics lessons). Mass, the amount of matter, does not change.
Important Facts
1
In chemistry, a substance is something with a defined chemical composition and properties.
2
Atoms consist of even tinier particles called protons, neutrons, and electrons.
3
Each element has its own symbol in the form of letters, and its own number that indicates the number of protons in its atom.
4
A chemical formula is a symbol for a substance that tells you which elements it is made of and how many atoms of each element it contains.
5
Substances change from state to another depending on their temperature.
6
The mass of an atom stays the same even when its state changes.
Vocabulary
Atom
Tiny particle made of protons, neutrons, and electrons
Atomic mass
The number of protons plus the number of neutrons in an atom
Atomic number
The number of protons in an atom
Attracted
Pulled together, like a magnet
Boil
The process of turning a liquid turns into a gas
Chemical composition
The specific elements that make up a substance
Chemistry
The study of what things are made of and how they change
Chemical formula
The symbol for a substance that tells you elements it is made of and how many atoms of each element its molecules contain
Composition
What something is made of
Compound
A substance made of atoms of more than one element
Condensing
The process of changing gas to liquid
Electrical charge
A force that contains electrical power and attracts an opposite electrical charge
Electrons
A part of an atom with a negative charge
Element
Substance made up of atoms of the same type
Freezing
The process of cooling liquid to change it into a solid
Mass
A measure of the amount of matter in a substance
Matter
Anything that has mass and volume
Melt
When a solid turns into a liquid
Molecule
More than one atom stuck together
Neutron
A part of an atom with no charge, or a neutral charge
Particle
A tiny, usually microscopic, piece
Properties
Qualities or characteristics of a substance, including how they look, feel, or behave
Proton
A part of an atom with a positive charge
Substances
All living and nonliving things; or (in scientific terms) matter with a defined chemical composition and properties
Volume
The size of something or how much space it takes up
Substances change between the phases depending on their temperature. Boiling, melting, condensing, and freezing are all processes that change a substance’s state.
Molecules connect together to form all kinds of substances. Depending on the properties of the matter and what temperature it is, substances can be in one of four states, or phases: gas, liquid, solid, and plasma.
In a gas, there is a lot of space between the molecules. Liquids have less space between molecules and can change shape. Both gases and liquids are fluids, which means they can change shape according to where they are. Solids have very little space in between the molecules. They cannot flow (move like fluid) and they have a more fixed shape.
Plasma is a hot gas with different properties. It is considered a fourth phase of matter, but we do not interact with it as often as the other three phases.
Look at the example of water. At room temperature, water is a liquid. If you heat water up, it becomes a gas (steam). And if you make it cold enough, it freezes and becomes a solid (ice).
Figure 12.3: This picture shows water in all three phases.
This picture shows water in all three phases.
Substances melt from solid to liquid and boil from liquid to gas. The changes can go in the other direction too. Condensing is what happens when a gas changes to a liquid. Freezing is the process that changes a liquid into a solid (like freezing water into ice). Different substances change their state at different temperatures, depending on what they are made of. Water freezes at 32 degrees Fehrenheit (0 degrees Celcius) but other substances might freeze at different temperatures.
Atomic mass
The atomic mass of an atom is the number of protons plus the number of neutrons that it contains.
The mass of an atom stays the same even when its state changes.
In science, especially chemistry and physics, the word mass has a very specific meaning. Mass is a property of matter and does not change.
The atomic mass of an atom is the number of protons plus the number of neutrons that it contains. (Some of the numbers are partial numbers, or decimals. That’s because the numbers of neutrons in an atom can vary, so the atomic mass number is an average). The mass of any one atom is the same no matter what the temperature is, what state it is in, or whether or not the atom is part of a molecule.
People often confuse mass with weight, which is how heavy something is. This is mostly because in English we often use the word weight when we actually mean mass, and the other way around. Weight can change because it depends on gravity (you will cover gravity in your physics lessons). Mass, the amount of matter, does not change.
Important Facts
1
In chemistry, a substance is something with a defined chemical composition and properties.
2
Atoms consist of even tinier particles called protons, neutrons, and electrons.
3
Each element has its own symbol in the form of letters, and its own number that indicates the number of protons in its atom.
4
A chemical formula is a symbol for a substance that tells you which elements it is made of and how many atoms of each element it contains.
5
Substances change from state to another depending on their temperature.
6
The mass of an atom stays the same even when its state changes.
Vocabulary
Atom
Tiny particle made of protons, neutrons, and electrons
Atomic mass
The number of protons plus the number of neutrons in an atom
Atomic number
The number of protons in an atom
Attracted
Pulled together, like a magnet
Boil
The process of turning a liquid turns into a gas
Chemical composition
The specific elements that make up a substance
Chemistry
The study of what things are made of and how they change
Chemical formula
The symbol for a substance that tells you elements it is made of and how many atoms of each element its molecules contain
Composition
What something is made of
Compound
A substance made of atoms of more than one element
Condensing
The process of changing gas to liquid
Electrical charge
A force that contains electrical power and attracts an opposite electrical charge
Electrons
A part of an atom with a negative charge
Element
Substance made up of atoms of the same type
Freezing
The process of cooling liquid to change it into a solid
Mass
A measure of the amount of matter in a substance
Matter
Anything that has mass and volume
Melt
When a solid turns into a liquid
Molecule
More than one atom stuck together
Neutron
A part of an atom with no charge, or a neutral charge
Particle
A tiny, usually microscopic, piece
Properties
Qualities or characteristics of a substance, including how they look, feel, or behave
Proton
A part of an atom with a positive charge
Substances
All living and nonliving things; or (in scientific terms) matter with a defined chemical composition and properties
Volume
The size of something or how much space it takes up
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