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As you have been told atoms are the smallest component of a substance that exists that retains it's own characteristics ( or properties). In the world, atoms can stay singular or can group together. If they group together, they act as one unit. How they group together is a function of subatomic particles (electrons, etc) in each of the atoms in the group. We will spend significant amounts of time and effort understanding how this occurs later in the class. So, for now, let us look at the 3 different grouping types:
1) Elements - no grouping type. Atoms are separate from each other. This is technically a lie since there are many elements that form groups (i.e. diatomic elements) and many that are metals so have metallic bonds (see below).
2) Ionic compounds - here is when atoms come together and their is a give and take of subatomic particles (specially electrons) to form ions (charge particles).
- Cation - positively charge atoms (lost electrons) and anion - negatively charged atoms (gained electrons).
- Cation and anion are held together due to Coloumbic force so the particle of Ionic compounds are ions.
3) Molecular compounds - here is when atoms come together and they share their electrons and stay together acting like one thing.
There is actually a 4th possible grouping called a Metal (what hold it together is called a metallic bond). There substance are made up of cations with a "sea of free-flowing electrons" between cations thereby coloumbic force keeps the cations and electrons near each other (also explains the properties of metals)..
There will be a lot more work on how, why and which atoms create these particle. But all matter (at least at your level of understanding) is composed of one of these grouping and have specific base units ( I call them particles)..
So to recap, (Note: IC - Ionic compounds and MC - Molecular compounds)
Base Unit or Particle
It is important to understand that all substance are composed of these particles.
This understanding of base units or particles provides the bases of knowing the difference between a physical process and a chemical reaction.
- Physically processes - particles (or atom groupings) do not change, you just changing the location of the particles compared to each other (getting them closer or farther away from each other).
- Chemical reactions - particles (or atom groupings) changes to create new particles (rearrange grouping of atoms) specifically by electron movement.