Chemistry:



Chemistry:

Compound, Mixture, Physical & Chemical Change

Physical Change – when the physical properties of a substance are altered (changed) without changing the identity of the substance.

Chemical Change – when a substance is changed into a new substance with different properties.

Density – a physical property of matter that is the mass per unit volume of a material. The formula for calculating density is density = mass divided by volume, D= m/v. The common units of density are grams per cubic centimeter, g/cm or grams per unit milliliter, g/ml.

Compound – when two or more elements combine chemically and form a new substance. Compounds have three important characteristics (properties): (1) Compounds have a definite composition (2) Compounds can be broken down into simpler substances by chemical means and (3) Compounds can be identified by their physical properties.

Mixture – a type of matter that forms when two or more substances are combined but do not join together chemically.

Molecule – the smallest unit of a compound that has all the properties of the compound.

Chemical Formula – the chemical symbols and subscripts used to identify the number of atoms of each element in a molecule of a compound. The make-up of molecules is shown in a chemical formula.

Atom – the smallest unit of an element that has all the properties of the element.

Element – a substance that cannot be broken down into simpler substances by ordinary chemical means.

Proton – a particle with a positive charge. Positive particle.

Neutron – a particle with no charge or neutral. Neutral particle.

Electron - a particle with a negative charge. Negative particle.

Note: Electrons are on the outside of the nucleus. Protons and Neutrons are on the inside of the nucleus. Every element has one or more energy levels where the electrons orbit the nucleus called the electron cloud.

Periodic Table – a chart that organizes information about all of the known elements according to their properties.

Atomic Mass – the number of protons and neutrons in the nucleus of one atom of the element.

Atomic Number – the number of protons contained in each nucleus of its atoms of the element.

Period – a horizontal row in the periodic table.

Group – a vertical column on the periodic table.

Reactivity – describes how likely an element is to form bonds with other elements.

Valence Electrons – electrons that are located in the outermost energy level of an atom.

Ion – an atom that has gained or lost one or more electrons.

Ionic Bond – a bond formed by the transfer of electrons (when valence electrons of one atom are transferred to the outer energy level of another atom).

Covalent Bond – a bond formed when two atoms share valence electrons.

Please copy the “Atomic Theory” below:

1) All matter is composed of atoms

2) Atoms of a given element are identical

3) Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

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