56 lines
1.9 KiB
Markdown
56 lines
1.9 KiB
Markdown
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---
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tags: [physics]
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---
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# Matter and atoms
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## Matter, elements, compounds and mixtures
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- Matter is anything that occupies space and has weight. It may be found in any
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one of three states: liquid, solid, or gas.
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- Matter can be classed in terms of **elements**, **compounds** and
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**mixtures**.
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- An element is a substance that cannot be reduced to a simpler substance by
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chemical means.
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- The chemical combination of two or more elements is a compound. Compounds
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_can_ be separated or reduced by chemical means but they cannot be
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physically separated.
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- A _physical_ (note not _chemical_) combination of elements and compounds is
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a mixture.
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- For example "air" is a mixture which is made up of oxygen, nitrogen, carbon
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dioxide, and other gases.
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## Atoms and molecules
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- Elements are made up of **atoms**.
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- A **molecule** is a type of compound where the atoms of two types of elements
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have joined together. For example sodium and chlorine are two elements that
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can join to form sodium chloride. We call this **chemical bonding**.
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## Atomic particles
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- There are three particles comprising atoms: **protons**, **neutrons** and
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**electrons**.
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- Protons and neutrons comprise the nucleus of the atom. A proton is positively
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charged. A neutron has no charge.
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- Electrons orbit around the nucleus in concentric rings. Electrons are
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negatively charged. Because of this protons and electrons attract each other.
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### Atomic number
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- The number of protons in the nucleus is called the element's **atomic**
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number.
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- We use the atomic number of elements to distinguish one element from another.
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### Atomic weight
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- The atomic weight of an atom is its mass.
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- The mass is determined by the number of protons and neutrons in the nucleus.
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- An electron $\frac{1}{1845}$ the mass of a proton. Its mass is so neglible
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that it makes no significant difference to the atomic weight.
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