Chemistry: Terms and Definition

Element

Robert Boyle defined this as the simplest composition of matter that cannot be broken down further by any chemical means. He also suggested that atoms of these combine to form different compounds.

Metalloids

It is a chemical element with properties that are in between, or a mixture of, those of metals and nonmetals.

• B, Si, Ge, As, Sb, Te, At, Po

Non-metals

It is a chemical element that lacks metallic attributes. They are poor conductors of heat and electricity, are physically brittle when in solid form, and tend to gain or share electrons during chemical reactions.

• Se, C, H, O, N, Cl, Br, I, F, P

• He, Ne, Ar, Kr, Xe, Rn

Metals

It is a chemical element that readily loses electrons to form positive ions (cations) and has atoms linked by metallic bonds.

Antoine Lavoisier

The Father of Modern Chemistry.

Law of Mass Conservation

In a chemical reaction, mass is neither created nor destroyed. The total mass of the reactants is equal to the total mass of the products.

• Mass of reactants = Mass of products

Law of Constant/Definite Composition

A given pure chemical compound always contain the same elements combined in the same fixed proportion by mass, regardless of the source or amount of the compound.

Law of Multiple Proportions

When two elements form more than one compound, the different masses of one element that combine with a fixed mass of the other element are in a ratio of small whole numbers.

Dalton’s Atomic Theory

1. All matter is composed of atoms, which are tiny, indivisible, and indestructible particles.

2. Atoms of the same element are identical in mass and properties, but different from atoms of other elements.

3. Atoms cannot be created, destroys, or subdivided in chemical reactions. They are conserved in reactions.

4. Compounds are formed when atoms of different elements combine in simple whole-number ratios.

5. In chemical reactions, atoms are rearranged to form new substances. Atoms are not created or destroyed.

Electron

It is a subatomic particle with a negative electric charge. It forms the outer layer of an atom, orbiting around the central nucleus.

• Symbol: e^-

• Relative Mass (amu): 0.0005

• Relative charge: -1

Proton

It is a subatomic particle with a positive electric charge located inside the nucleus at the center of an atom.

• Symbol: p⁺

• Relative Mass (amu): 1

• Relative charge: +1

Neutron

It is a subatomic particle with no electric charge (neutral) that sits alongside protons inside the atomic nucleus.

• Symbol: n⁰

• Relative Mass (amu): 1

• Relative charge: 0

Mass Number (A)

The total number of protons and neutrons found in the nucleus of an atom.

• p⁺ + n⁰

Atomic Number (Z)

The number or proton in the nucleus of an atom. It tells the identity of the element.

Ion

It is when a neutral atom gains or loses one or more electrons.

Atom

It is the smallest unit of matter that retains the identity and properties of an element.

Molecule

It is a group of two or more atoms that are chemically bonded

Cations

Metal tends to lose electrons and become positively charged.

Anions

Nonmetals gain electrons and becomes negatively charged.

Isotopes

Atoms of the same element that have the same number of protons but different number of neutrons.

Ionic Compound

Compounds formed through the transfer of electrons, resulting in the attraction between positively and negatively charged ions.

Covalent Compound

Compound formed when atoms share electrons to achieve stable electron configurations.

Protium

The most common isotope of hydrogen, containing one proton and no neutron.

• Hydrogen-1

Deuterium

An isotope of hydrogen containing one proton and one neutron.

• Hydrogen-2

Tritium

An isotope of hydrogen containing one proton and two neutron.

• Hydrogen-3

Hydrated Salt

Compounds that contain a definite number of water molecules chemically incorporated into their crystal structures.

Percentage Abundance

The percentage of a particular isotope found in a naturally occurring sample of an element.

Atomic Mass

Weighted average of the isotopes mass and its percentage abundance. It is expressed in atomic mass units (amu).

Molecular Mass

The sum of the atomic masses of all atoms present in a molecule.

Combustion

The process of burning a substance (usually fuel) in the presence of oxygen to produce CO₂ and H₂O, releasing energy in the form of heat and light.

Complete Combustion

• Hydrocarbon fuel happens when there is a good or sufficient supply of air or oxygen.

• Carbon Dioxide and water are produced.

Incomplete Combustion

• Happens when the supply of air of oxygen is poor or insufficient.

• Less energy is released.

Positive Impacts of Combustion in the Environment

• Energy production

• Cooking and heating

• Industrial application

• Waste disposal

• Rocket Propulsion

Negative Impacts of Combustion in the Environment

• Air pollution

• Greenhouse Gas Emissions

• Health Hazards

• Resource Depletion

• Environmental Damage

• Explosion and Fire Hazards

Molecular Formula

A chemical formula that represents the actual number of atoms of each element present in one molecule of a compound.

• C₈H₁₈ - Octane

Structural Formula

A chemical formula that shows how of atoms are arranged and connected to one another through chemical bonds.

Condensed Formula

A simplified representation of a structural formula in which most or all bond lines are omitted and atoms are writtten in groups to indicate their connectivity.

• CH₃(CH₂)₆CH₃

Empirircal Formula

A chemical formula that represents the simplest whole-number ratio of atoms of different elements in a compound.

• C₈H₁₈ -> C₄H₉