Structure of an Atom

What Is an Atom? Atoms are often referred to as the building blocks of matter. Each element on the periodic table is composed of one type of atom and cannot be broken down into a simpler substance. Structure of the atom. (n.d.). Retrieved from http://www.nyu.edu/pages/mathmol/textbook/atoms.html

What Is an Atom? Atoms are composed of smaller subatomic particles such as the proton, neutron, and electron. Atoms contain a nucleus surrounded by an electron cloud that consists of one or more energy levels.

Inner Structure of an Atom Nucleus - Small, dense, positively charged center of the atom which contains most of the atom’s mass

Inner Structure of an Atom The nucleus contains the following subatomic particles: Protons - positively (+) charged particles, determines element’s identity, contributes to mass, amu=1 Neutrons - particles that have no charge (neutral), but contribute to the atom’s mass, amu=1

Outer Structure of an Atom Electron cloud - an area around the nucleus where electrons are likely to be found orbiting the nucleus in several energy levels

Outer Structure of an Atom The electron cloud contains several energy levels Electrons - negatively (-) charged particles located in specific energy levels surrounding the nucleus amu-almost zero

Outer Structure of an Atom Multiple energy levels in the electron cloud completely surround the nucleus. Electrons follow a specific order to fill the energy levels. Maximum of 2 electrons Nucleus Maximum of 8 electrons Maximum of 8 electrons* *Applies to the first 18 elements only

Outer Structure of an Atom The electrons in the outermost energy level are called valence electrons The shell containing electrons that is furthest from the nucleus is called the valence shell The number of electron shells with electrons is the same as the period number on the Periodic Table.

Valence Electrons Electron Shell Number of Electrons 1 2 8 3 4 18 5 6 Each electron shell can hold a certain number of electrons Electron shells are filled from the inside out Noble Gases have full outer electron shells All other elements have partially filled outer electron shells Electron Shell Number of Electrons 1 2 8 3 4 18 5 6 32 7

Noble Gas Stability Noble gases are usually unreactive This is because they have full valence shells An element with a full valence shell is a happy element  For two atoms to join together atoms must gain, lose or share electrons Elements with full valence shells do not easily gain or lose electrons

Atomic Stability Atoms want to gain stability Atoms will try to gain or lose electrons to have a full valence shell Metals try to lose electrons Non-Metals try to gain electrons

Decoding Atom Information from the Periodic Table Carbon 6 12.0 Atomic Number Atom’s Symbol Atom’s Name Atomic Mass

Decoding Atom Information from the Periodic Table Atomic number # of protons = # of electrons 6 C Carbon Atomic mass = # of protons plus the # of neutrons 12.0

Atom Characteristics The number of protons in the nucleus is the atomic number of that atom. Protons are used to identify elements. The atomic number represents the number of protons (+) and is equal to the number of electrons (-).

Atom Characteristics The atomic mass is the mass of the protons plus the mass of the neutrons. So, the mass is determined by the nucleus only Atomic mass is recorded in the SI units: atomic mass units (amu). Protons and neutrons each are given an amu of 1. Electrons have a mass of nearly zero. Structure of the atom. (n.d.). Retrieved from http://www.nyu.edu/pages/mathmol/textbook/atoms.html