Chemistry Unit 2

Subatomic Particles:




1.)Positively charged (each proton has a +1 charge). Found in nucleus of atom. Each nucleus must contain at least 1 proton. Mass = 1 a.m.u. (atomic mass unit)

2.)Has no charge (neutral). Found in nucleus. Mass of neutron is = to mass of proton (Mass = 1 a.m.u.)

3.)Negatively charged (each electron has a -1 charge). Found around the nucleus of an atom (energy levels in electron cloud). Mass = 1/1837 a.m.u. (due to the extreme lightness of the electron, it is not factored when determining the mass #. However, it will be accounted for in the atomic mass which can be found on the periodic table)

Each element square on the periodic table includes:


2.)Atomic #

3.)Atomic mass

1.)one or 2 letters that represent the name of the element (first letter is capitalized; 2nd is lower cased)

2.)the number above the symbol that tells you the number of protons (and electrons in a neutral) atom. The atomic # tells you the number of protons, which determines the element!

3.)the number below the symbol that gives you the atomic mass of the atom (accounts for the mass of protons, neutrons AND electrons of naturally occurring isotopes for any given element)


Mass Number

the # of protons + the # of neutrons


one of 2 or more forms of the same element which differ in the number of NEUTRONS

ex.)Carbon-12: mass# is 12 = 6 protons, 6 neutrons and 6 electrons

Carbon-14: mass# is 14 = 6 protons, 8 NEUTRONS, and 6 electrons

Average Atomic Mass

Take into account of ALL of the isotopes that exist and the percentages(%) of each type

ex.) Cl-35: 75.4% & Cl-37: 24.6%

((35amu x 75.4) + (37amu x 24.6))/100 = 35.49amu!!




atom with a charge (positive or negative) due to loss or gain of electrons

1.)POSITIVE ion due to LOSS of one or more electrons 2.)NEGATIVE ion due to GAIN of one or more electrons

*Note: positive and negative charges are attracted to each other!

Niels Bohr

created an atomic model that resembled a solar system with planets revolving around the sun.


Energy Levels

The energies electrons can have. Electrons move with constant speed in fixed orbits around the nucleus. Each electron has a specific energy and if an atom gains or loses energy, the energy of an electron can change.

Bohr’s Explanation

Electrons can circle the nucleus only in allowed paths called “orbitals”. The only way an electron may move out of its orbit is by gaining an amount of energy equal to the difference in energy between a higher-energy orbit and the initial lower-energy orbit. When an atom falls back down (from the “excited state” to the “ground state”) a photon (bundle of) energy is emitted that has energy equal to that initially gained in the “quantum jump”

Equation for # of electrons allowed in each energy level:

2n2 (n = energy level: 1,2,3,4, etc)

ex.) 1st energy level = 2 electrons

2nd energy level = 8 electrons

3rd energy level = 18 electrons

4th energy level = 32 electrons

Evidence for energy levels

Energy gained or energy released can be measured when an electron moves energy levels – movement between electrons between energy levels explains the light emitted in fireworks (when going back to ‘ground state’). Heat produced by the explosion causes electrons to move to higher energy levels. When electrons move back down, they emit energy in the form of visible light. Different elements emit different colors of light.

Electromagnetic Radiation

A form of energy that exhibits wave-like characteristics as it travels through space. It is produced by the motion of electrically charged particles and it radiates from electrically charged particles.

Tagged In :

Get help with your homework

Haven't found the Essay You Want? Get your custom essay sample For Only $13.90/page

Sarah from studyhippoHi there, would you like to get such a paper? How about receiving a customized one?

Check it out