Atomic Number = Number of Protons
Atoms are neutral, so the number of protons would be equal to the number of electrons. The charge would be 0.
Atomic mass = #protons + #neutrons
Protons and neutrons have the same mass, which is 1800 times bigger than the mass of electrons.
Example: Oxygen (O) has an atomic mass of 16, atomic number of 8, 8 protons, and 8 neutrons.
Bohr's Model of Electron Arrangement
1913 - Bohr explains movement of electrons around the nucleus of an atom.
Electrons orbit the nucleus.
Each orbit is a certain distance from the nucleus.
Each orbit has a definite energy level.
Each orbit has a definite number of electrons. (2, 8, 8, 18...)
Nitrogen (N) atom has 7 protons and 7 electrons.
Phosphorus (P) +3 ionic charge would make 12 electrons and 15 protons.
Valence shell: the outer shell of electrons
Valence Electrons: electrons in the outer shell
Valence: number of electrons in the outer shell
Drawing Bohr Model Diagrams
For example: A neon atom would have an atomic number of 10, 10 protons, 10 electrons, 2 electron shells, and an ion charge of 0.
A fluorine ion would have an atomic number of 9, 9 protons, 10 electrons, 2 electron shells, and a -1 ion charge (electrons to protons.)
Elements: Names and Symbols
More Notes: Bohr Models and Stability
Most elements in the same family have the same number of valence electrons.
Elements in the same period have valence electrons in the same shell.
The period number indicates the number of shells that have electrons.
The number of electrons in a shell corresponds to the number of elements in that period.
Atoms become stable when they have a full outer shell of electrons.
Noble gases are un-reactive because they have full outer shells of electrons.
Atoms in other families will gain or lose electrons to have a full outer shell.
Having an uneven number of protons and electrons gives an atom a charge and makes it an ion.
Metals lose electrons to become positive ions.
Nonmetals gain electrons to become negative ions.
Charge of an ion = sum of the charges of protons and electrons (electrons to protons)
Ions are written as the chemical symbol with a superscript of their charge.
Elements and Symbols
Elements are made of one kind of atom. They are represented by chemical symbols consisting of one or two letters. Each element has a unique set of properties. There are only 2 elements that are liquid at room temperature: bromine and mercury.
Elements may be classified as nonmetals, metals, or metalloids. Metals are elements that are shiny, ductile, malleable, and good conductors of heat or electricity. Nonmetals are elements that are dull, not ductile, brittle, and poor conductors of heat or electricity. Metalloids have properties of both. Nonmetals are grouped on the right, while metals are on the left of the zigzag line forming at the left of Boron.
The Periodic Table of the Elements
Mendeleev suggested arranging the chemicals by physical properties and increasing atomic mass.
Elements are arranged according to their physical properties and increasing atomic mass. Metalloids (elements near the zig zag line) consist of B, Si, As, Te, At, Uuo, Ge and Sb. Vertical columns: families or groups that have numbers, determine the number of valence electrons. Horizontal rows: periods that determine the number of electron shells.
Group 1: Alkali metals, most reactive
Group 2: Alkaline earth metals
Groups 3-12: Transition metals
Groups 3-6: named after first element in the family
Group 7: Halogens, never found in pure form in nature, highly reactive with the alkali metals, most reactive non-metals
Group 8: Noble gases, most unreactive
Hydrogen has separate properties from all other families but is often placed in Group 1.