2nd Class

Basic Chemistry

During our second class, we review few basic chemistry topics, such as elements, compounds, and bonds between atoms.

Atomic number = # of protons = number of electrons

Atomic mass number = protons + neutrons

Atomic mass number – Atomic number = neutrons

Elements VS Compounds:

 

1. Elements: Elements are substances that cannot be separated into simpler substance.

2. Compounds: A compound is a substance formed when two or more elements are chemically joined.

 

Compound VS Molecule

1 A molecule consists of two more atoms, which can be the same or different types of atom, that are linked by a chemical bond. A molecule of H2 or O2 is still a molecule, but not a compound.

2. A compound is usually a molecule as well. To be a compound, it has to have two different types of atoms, such as H2O.

3. Some compounds like NaCl are not molecules because they are linked together in a crystalline structure, rather than being molecularly bonded.

Isotope:

Isotope: one of two or more atoms with the same atomic number but with different numbers of neutrons. Some isotopes are very useful in the field of chemistry and biology. One example would be radiation. Radiation from certain isotopes can be used to detect and treat cancer while also kill bacteria.

Nonpolar covalent VS Polar covalent VS Ionic bonds.

1. A nonpolar covalent bond is a bond where electrons are shared equally between two atoms.

2. A polar covalent bond is a chemical bond where the shared electrons spend more time closer to the nucleus of the more electronegative atom.

3. In an ionic bond, the electrons are completely transferred from one atom to another rather than shared.