The Structure of the Atom

Modern Concept of Atomic Theory 1.Atom consists of a tiny nucleus 2.Electrons move in an area directly surrounding the nucleus which is called an ORBITAL.

NUCLEUS Contains protons —Positively charged —Relative mass = 1836 amu Contains neutrons —No charge —Relative mass = 1839 amu Protons and neutrons are about the same mass

NUCLEUS The nucleus accounts for only a small portion of the atom’s volume BUT Contains the majority of the atom’s mass

ORBITAL Contains electrons —Negatively charged —Relative mass = 1 amu The orbital accounts for the majority of the atom’s volume BUT Contains only a small portion of the atom’s mass

Electrons Electrons move randomly Electrons cannot be shown to be at any one location at any one time Electrons can only be shown to be in a probability map of where they could be Negatively charged electrons tend to stay close to the nucleus because of their attraction to the protons positive charge

Atomic Chemical Properties Atoms have different chemical properties because of the number and arrangement of the electrons – Electrons are the parts of the atoms that combine with other atoms to form molecules

Atomic Number Is basically the number of the element on the periodic table It also determines the number of protons in the nucleus Number of protons = atomic number

Atomic Mass The mass of the atom This is calculated by averaging the exact weight of every naturally-occurring stable isotope of that atom in nature based on the percent abundance of that atom in nature. Example: Carbon ( )(0.9890) + ( )(0.0110) = amu Mass NumberExact weight% abundance

Mass number The rounded form of the atomic mass Gives the amount of protons & neutrons combined Using the atomic number as well, you can calculate the number of neutrons in the nucleus Number of neutrons = Mass number – atomic number

Nuclear Symbol By knowing the element symbol, atomic number, and mass number, you can write the nuclear symbol of an element