Atomic Structure

Atomic Structure

·         Subatomic Particles

Neutrons- large with no charge

Proton- large with positive charge

Electron- small with negative charge

Name	Symbol	Relative Mass (Atomic Mass Unit, AMU)	Electric Charge	Location in the Atom
Proton	1p 1	1	+1	Nucleus
Neutron	1n 0	Slightly >1	0	Nucleus
Electron	0   e −1	≈0	-1	Cloud surrounding the nucleus

·         In a neutral atom,

Number of protons = Number of electrons (overall charge is 0)

·         Atomic Number = # of protons = # of electrons

·         If a proton is added to an element’s nucleus, a new element will be produced.

For example, O add one proton, atomic mass from 16 to 17, atomic number from 8 to 9

·         Ions- Atoms that gain or lose electrons

Number of electrons = protons – charge

·         Negatively-charged ion (anion): add a electron (electrons more than protons)

·         Positively-charged ion (cation): lose electrons (protons more than electrons)

·         Mass Number (A): is the total number of protons and neutrons or atomic mass number.

Since Atomic Number = The # of protons, Atomic mass = # of protons + # of neutrons

Number of Neutrons = Mass Number –Atomic Number

Atomic Mass ≈ Mass Number

·         Isotopes are atomic species having the same atomic number (protons) but different atomic masses/mass numbers (neutrons).

·         The molar mass represents an average value of a mixture of isotopes.

Example: Cl-35 = 75.77% and Cl-37 = 24.23%

Average mass = (0.7577 x 35) + (0.2423 x 37) = 35.49 g/mol

April 20--Electronic Configuration

Eletronic Configuration is of an atom is notation that desctibes the orbitals in which the electrons  occupy and the total number of electrons of electrons in eaqch orbital.


Niels Bohr proposed that electrons only exist in specific energy states.
1. ground states -when all the electrons of an atom are in their lowest possible energy levels
2. excited states-when on or more of atoms electrons are in energy level.


-Energy level is the amunt of energy, which an electon in an atom can possess.( n is the of energy level)
-The difference between two particular energy level is called quantum of energy.


An orbital is the actual region of space occupied by an electron in a particular energy level.
A shell is the set of all orbitals having the same n-value.
A subshell is a set of orbitals of the same type.


-The letter S,P,D,F-four different types of orbitals and for each value of n,there is a different type of orbitals
n=1 only s-type                                  one
n=2 s-type,p-type                               three
n=3 s-type, p-type,d-type                    five
n=4 s-type,p-type,d-type,f-type           seven
*A maximum of 2 electrons can be placed in each orbit


The order in the orbital:

Writing Electronic Configuration for Neutral Atoms
1. start with the lowest energy level
2.calculate how many electrons you have(neutral atoms=atomic number),then start with 1s and just keep adding until none left behind
3.each electron is represent by up and down arrow

Writing Electron Configurations for ions
For negative ion
 -Add electrons equal to the charge to the last unfilled subshell
For positive ion
-start with the neutral configuration, remove electrons from the outermost shell first.
-if the s and p are electrons in both of the outermost shell, the electrons in the p-orbitals are removed first


Core Notation
using the core and the outer electrons to show the electron configuration
1. located the atom on the period table and note the noble gas at the end of the row above the element
2.replace the electrons with noble gas


eg.   S   1s2 2s2 2p6 3s2 3p4the first three parts replaced by noble gas Ne       [Ne] 3s2 3p4


*exceptions   Cu and Cr 

Trends on the Periodic Table

Elements close to each other on the periodic table display similar characteristics.

Metallic Properties:

- from left to right across the table = metallic to non-metallic

- going down a family in the table = more metallic

Atomic Radius
<the measure of the size of an atom>

- going across a row left to right = atomic radii decreases

- going down a group = atomic radii increases

Reactivity
<the rate at which a chemical substance tends to undergo a chemical reaction> 

- Metals and non-metals have different trends.

(The most reactive metal is Francium, and the most reactive non-metal is Fluorine.)

Ion Charge

- Each group (column) in the periodic table have different ion charges.

Melting Point
 <the temperature of a solid at which it changes state from solid to liquid>

- Elements in the center of the table have the highest melting point.

- Noble gases have the lowest melting/boiling points

- Melting point increases from the left to right of the table until the middle.

Ionization Energy

<The energy required to remove an electron from a neutral atom, measured in kJ/mol.>

- increases going up and to the right

- Helium has the highest ionization energy, and Francium has the lowest ionization energy.

Electronegativity

<The tendency of an atom to attract electrons from a neighbouring atom>

- increases going up and to the right

- Fluorine is the most electronegative element in the periodic table