Pure Chem-Atoms+Elements+Compounds+Isotopes+Ions+Ar

Elements

-An element is a pure substance made up of only one type of atom. (e.g. oxygen, carbon)

-Represented by chemical symbols like “O” for Oxygen or “H” for Hydrogen

-About 118 known elements

-Cannot be broken down into simpler substances

Compound

-Two or more different elements chemically bonded in a fixed ratio. (e.g. H2O, CO2)

-Represented by chemical formulas such as H2O for water or CO2 for Carbon Dioxide

-Cannot be separated physically

-Chemical reactions are needed to break compounds into their individual elements

Mixtures

-Two or more elements or compounds physically mixed, not chemically bonded; can be separated by physical methods (e.g. filtration, distillation)

-Components in a mixture retain their individual properties

-Can be seperated by physical means

Key differences:

• Elements: one type of atom, cannot be broken down by chemical means.

• Compounds: can only be broken down into elements by chemical reactions.

• Mixtures: properties of parts stay the same; can be separated physically.

Atoms v.s. Molecules

Atom - smallest indivisible unit of an element

Molecule - group of atoms bonded together (can be made of the same or different elements)

Molecules v.s. Compounds

A compound is a specific type of molecule. Not all molecules are compounds.

Substances

Substances made of 1 type of atoms are called elements.

→ Atoms

→ Molecules

Substances made of more than one type of atoms are called compounds.

Mixtures are made of two or more elements or compounds not chemically bonded together.

Atomic Structure and the Periodic Table

Atoms:

  • smallest unit of matter that makes up everything around us

  • basic building blocks of all substances

  • come in different types known as elements

Consist of subatomic particles known as:

  1. Protons

  2. Neutrons

  3. Electrons

Nucleus

  • the nucleus is the central core of an atom

  • contains two types of subatomic particles

    • Protons-positively charged particles

    • Neutrons-electrically neutral particles

  • Electrons are negatively charged particles that orbit the nucleus in shells

    • much lighter in mass

  • Electron shells

    • electrons are arranged in energy levels or electron shells around the nucleus

Atomic Structure:

  • center called the nucleus with neutrons and protons

  • electrons arranged in energy levels or shells

  • electrons orbit the nucleus

Proton Number

  • the proton number or atomic number is the number of protons in the nucleus of an atom

  • the number of protons are always equal to the number of electrons in a neutral atom

  • the atomic number also helps us identify where the element is located on the periodic table

Each type of atom is characterised by its unique number of protons.

Smaller of the two numbers, whereas on place.

Mass Number

  • the mass number or nucleon number is the total number of protons and neutrons in the nucleus of an atom

  • it represents the total mass of the atom

  • relative atomic mass is not the same thing as mass number

Relative atomic mass v.s. mass number

Relative atomic mass is the average mass of all the isotopes of an element.

Mass number is the total number of protons and neutrons in an element.

Calculating relative atomic mass

Relative Atomic Mass (Ar) is the average mass of all the isotopes of an element compared to 1/12th of the mass of a carbon-12 atom.

The fixed mass of a carbon-12 atom is like a standard reference point for comparing the masses of all other atoms.

Figuring out Ar

We figure out Ar by looking at the relative masses of each isotope and how common each isotope is (it’s abundance).

Increase the number of terms added based on the number of isotopes

Relative atomic mass is rounded to the whole number except for chlorine.

*For most cases, you can use relative atomic mass as a substitute for mass number, except for Chlorine.

Calculating Neutrons

Mass number/Nucleon number - Proton number/Atomic number = Neutron number

Electron Configuration

  • way of describing how electrons are arranged in an atom

  • electrons are arranged in shells around the nucleus

  • each shell can hold a certain amount of electrons

1st shell: 2 electrons

2nd shell: 8 electrons

3rd shell: 8 electrons

How to write the electron configuration of the element:

  1. Atomic number of the element

  2. Arrange the electrons taken into account with maximum electron number in each shell

  3. Shown using shell diagrams or notation

Ions

Ions: atoms with net electric charge due to the gain or loss of electrons

Electron Configuration of Ions

Atoms become ions because they want a stable, full, outer shell of electrons.

This can be achieved in two ways:

  1. Taking in electrons

  2. Giving away

For example: Sodium (NA)

Sodium has an electron configuration of 2,8,1.

It has 1 electron in its outer shell.

To achieve full outer shell, they can:

  1. Lose 1 electron so they have a full outer shell of 8 electrons

  2. Gain 7 electrons so they can have another full outer shell of 8

Simpler option: 1 - Losing 1 electron

Sodium will give away its extra electron to achieve a full outer shell.

Sodium ion electron configuration: 2,8

Periodic Table

Columns: numbered using roman numerals from 1-8 (groups)

Rows : numbers using digits from 1-7 (periods)

Group 8 - Noble Gases

  • They have full outer shells

  • Highly stable/inert

  • Do not react with other elements because they are satisfied with their electron configuration

The number of outer shell electrons is equal to the group number in Groups I to VIII.

The number of occupied electron shells is equal to the period number of 1-7.

Isotopes

Isotopes: different atoms of the same element that have the same number of protons but different numbers of neutrons.

Same atomic number but different mass number.

Same chemical properties because they have the same number of electrons.

Same electronic configuration.

Example:

Carbon - 12 and Carbon - 14