Chemistry (efnafræði)

Matter is anything that occupies space and has mass.

• A substance is matter that has a definite or constant composition and distinct properties.
• Efnismassi sem hefur vel skilgreinda samsetningu eða eðliseiginleika.

A mixture is a combination of two or more substances in which the substances retain their distinct identities.

• The combination of the mixture is the same throughout the solution.
• Samsetning er eins allsstaðar, óháð stað og stund.
• Example: Sodium chloride in water.

• The composition is not uniform.
• Samsetningin er háð stað og stund.
• Example: viður, blóðsýni, mjólk o.s.fr.

• Compound is a substance composed of two or more elements chemically united in fixed proportions.
• Efni sem eru samansett úr tveimur eða fleiri frumefnum sem eru tengd innbyrgðis í ákveðnum hlutföllum.
• Example: Vatn (H₂O), ammoníak (NH₃), glúkósi (C₆H₁₂O₆).

• Physical property can be measured and observed without changing the composition (samsetning) or identity of a substance.
• Eiginleiki sem tengist eðlishegðun efnis án þess að samsetning þess breytist.
• Example: suðumark, bræðslumark, eðlismassi, litur.

• To observe chemical property we must carry out a chemical change.
• For example the statement "Hydrogen gas burns in oxygen gas to form water" describes a chemical property.
• Efnaeiginleiki felst í samsetningu efnis, efni hvarfast og breytist í annað efni (sem hefur aðra eðliseiginleika).

• 1. Elements are composed of extremely small particles, called atoms. (All matter is made of matter).
• 2. All atoms of a given element are identical, having the same size, mass, and chemical properties. Atoms of one element are different from the atoms of all other elements.
• 3. Compounds are composed of atoms of more than one element.
• 4. Chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.
• 5. Atoms can not be subdivided, created or destroyed.

Isotropes are atoms with the same atomic number but different mass numbers. Because of the different numbers of neutrons.

Mass number = number of protons + number of neutrons

One atomic mass; a mass exactly equal to one-twelfth the mass of one carbon-12 atom.

• Electron (e^-):
• Mass = 9.10938*10^-28  
• Coulomb = -1.6022*10^-19
• Charge unit = -1

• Proton (p⁺):
• Mass = 1.67262*10^-24
• Coulomb = +1.6022*10^-19
• Charge unit = +1

• Neutron (n⁰):
• Mass = 1.67493*10^-24
• Coulomb = 0
• Charge unit = 0

Ionic bond: the electrostatic force that holds ions together in an ionic compound.

Covalent bond: a bond in which two electrons are shared by two atoms. 

Coordinate covalent bond: a covalent bond in which one of the atoms donates both electrons.

Mercury (Hg) and bromine (Br₂)

H₂, N₂, O₂, O₃, F₂, Cl₂, He, Ne, Ar, Kr, Xe, Rn.

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

For every action there is an equal and opposite re-action.