Atoms, Molecules, and Ions
Atom
An atom is the smallest particles of an element that
retains the chemical properties of the element. So we're talking some
super-tiny stuff here. Atoms are
electrically
neutral, with a positively charged nucleus that binds one or more
electrons in motion around it.
Atomic Number (Z)
The atomic number is the number of protons in an
atomic nucleus. In an elemental symbol the atomic number is a leading
subscript. For example, in 126C the 6 is the atomic number.
Atomic Theory
The atomic theory is an explanation of chemical
properties and processes that assumes tiny particles called atoms are the
ultimate building blocks of matter.
Atomic Symbol
The atomic symbol is the letter or set of letters
internationally agreed upon for a chemical element. For example, C is the
atomic symbol for carbon.
Cation
A cation is a positively charged ion. Metals typically
form cations.
Chemical Formula
A chemical formula is a representation of a substance
using symbols for its constituent elements. It is chemistry shorthand.
Compound
A compound is a material formed from elements
chemically combined in definite proportions by mass. For example, water is
formed from chemically bound hydrogen and oxygen. Specifically, a single
compound of water is made up of two hydrogen atoms and one oxygen atom.
Diatomic
A diatomic molecule is a molecule that contains only
two atoms. All of the noninert gases occur as diatomic molecules. Hydrogen,
oxygen, nitrogen, fluorine, and chlorine exist as H2, O2, N2, F2, and Cl2,
respectively.
Electron
An electron is a fundamental constituent of matter
having a negative charge and negligible mass.
Empirical Formula
An empirical formula is the simplest of all formulas.
Empirical formulas show which elements are present in a compound, with their
mole ratios indicated as subscripts in their smallest whole number ratios.
Ion
An ion is an atom or molecule that has acquired a
charged by either gaining or losing electrons. An atom or molecule with missing
electrons has a net positive charge and is called a cation. An atom or molecule
with extra electrons has a net negative charge and is called an anion.
Ionic Compound
Anion
An anion is a negatively charged ion. Non-Metals
typically form anions.
An ionic compound is also called a salt. It is a
compound composed of cations and anions held together by electrostatic forces.
Law Of Conservation Of Mass
The law of conservation of mass states that there is
no change in total mass during a chemical reaction.
Law Of Definite Proportions
The law of definite proportions states that when two
pure substances react to form a compound, they do so in a definite proportion
by mass. For example, when water is formed from the reaction between hydrogen
and oxygen, the definite proportion is 1 g of H for every 8 g of O.
Law Of Multiple Proportions
The law of multiple proportions states that when one
element can combine with another to form more than one compound, the mole ratios
of the elements in the compounds are simple whole-number ratios of each other.
For example, in CO and in CO2, the oxygen-to-carbon mole ratios are 1:1 and 1:2
respectively.
Mass Number (A)
The mass number is the total number of protons and
neutrons in an atom or ion.
Molecular Formula
The molecular formula is a notation that indicates the
type and number of atoms in a molecule. For example, the molecular formula of
carbon dioxide is CO2.
Molecule
A molecule is a collection of chemically bound atoms with
characteristic composition and structure. Making or breaking bonds in a
molecule changes it into a new molecule.
Monatomic Ion
A monatomic ion is an ion composed of a single atom.
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