Structure of an Structure of an AtomAtom

What Is an Atom?What Is an Atom?An atom is often referred to as the building block of matter. Atoms have a nucleus surrounded by an electron cloud

Atoms are composed of smaller subatomicsubatomic particles in an atom. The protonproton, neutron neutron, and electronelectron.

Each elementelement is composed of one type of atom and can not be broken down into a simpler substance

Inner Structure of an Inner Structure of an Atom Atom

• Nucleus - Small, dense, positively charged center of the atom which contains most of the atom’s mass

• The nucleus contains subatomic particles that have certain characteristics:Protons Protons ((p+) - positively charged particles in the nucleus of the atom, contribute to the atom’s mass

NeutronsNeutrons (no)- particles in the nucleus that have no charge, but contribute to the atom’s mass NEUTRAL

Outer Structure of an Outer Structure of an AtomAtom

●Electron cloud Electron cloud - an area encircling the nucleus where electrons are likely to be found●The cloud contains energy levelsenergy levels electrons electrons ((e-)are negatively charged particles located in specific energy levels

energy levels completely surround the nucleus

there is a specific order for the electrons to fill the energy levels

Outer Structure of an Outer Structure of an AtomAtom●Energy levels Energy levels completely surround the nucleus

Maximum of 2

electrons

Nucleus

Maximum of 8

electronsMaximum of 18

electrons

Maximum of 32

electrons

Maximum of 50

electrons

Outer Structure of an Outer Structure of an AtomAtom●valence electrons valence electrons are in the outermost energy level and are the electrons involved in bondingvalence electrons determine the number of bonds an atom can form

an atom is most stable when its outermost energy level is full

Atom CharacteristicsAtom CharacteristicsThe number of protons in the nucleus is the atomic number atomic number of that atom.

The number of protons (+) equals the number of electrons (-) in a neutral atom

The mass number mass number is the mass of the protons plus the mass of the neutronsmass is reported in the SI units atomic mass units atomic mass units (amuamu)

Protons and neutrons each are given an amu of 1

Electrons have a mass of nearly zero

Decoding Atom Decoding Atom Information Information

Ccarbon

6

12.011

Symbol

Name

# of proton

s

Atomic mass

Decoding Atom Information: Decoding Atom Information:

carbon

12.0112.0111

# of protons = # of electrons in a neutral atomAtomic mass is

a weighted average of all the isotopes of an element

66

C

The mass number of an atom is for a particular isotope of that element

Mass number is the total number of protons and neutrons in the nucleus

Example for C-12:◦6 protons + 6 neutrons= 12◦12 is the mass number for Carbon-12

*13 is the mass number for Carbon-13 and comes from C-13 having 6 protons and 7 neutrons