electron configuration is the arrangement of electrons of an atom, a molecule
Shells -The electron shells are labelled K, L, M, N, O, P, and Q; going from innermost shell outwards. -Electrons in outer shells have higher average energy and travel farther from the nucleus than those in inner shells.
Subshells -Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals.
- Example: The first (K) shell has one subshell, called "1s"; the second (L) shell has two subshells, called "2s" and "2p"; the third shell has "3s", "3p", and "3d"; and so on.
Each s subshell holds at most 2 electrons
Each p subshell holds at most 6 electrons
Each d subshell holds at most 10 electrons
Each f subshell holds at most 14 electrons
Each g subshell holds at most 18 electrons
Notation -Notation consists of a sequence of atomic orbital labels (e.g. for phosphorus the sequence 1s, 2s, 2p, 3s, 3p) with the number of electrons assigned to each orbital (or set of orbitals sharing the same label) placed as a superscript.
-Examples:
Hydrogen : 1s1 (has one electron in the 1s-subshell)
Valence Electron
-the electrons in the last shell or energy level of an atom - the electrons of an atom that can participate in the formation of chemical bonds with other atoms -The valence electrons increase in number as you go across a period
Periodic table group
Valence
electrons
Group 1 (I)
1
Group 2 (II)
2
Groups 3-12
See note *
Group 13 (III)
3
Group 14 (IV)
4
Group 15 (V)
5
Group 16 (VI)
6
Group 17 (VII)
7
Group 18
8**
* The general method for counting valence electrons is generally not useful for transition metals. Instead the modified d electron count method is used.
** Except for helium, which has only two valence electrons.
-Example: Valence electron of Phosphorus(1s2 2s2 2p6 3s2 3p3) : 2+3 = 5
Core Notation
- Instead of writing out all of the electrons in the configuration, you can write out just the ones since the last noble gas
-Example: electron configuration of Magnesium is 1s 2 2s 2 2p 6 3s 2 ---->［Ne］3s 2
Ground State -The condition of an atom, ion, or molecule, when all of itselectronsare in their lowest possible energy levels, not excited. -When an atom is in its ground state, its electrons fill the lowest energyorbitals completely before they begin to occupy higher energy orbitals, and they fillsubshellsin accordance with Hund's rule
Excited State -An excited state is any state with energy greater than the ground state
-Excited states tend to have short lifetimes; they lose energy either through collisions or by emitting photonsto "relax" back down to their ground states.
Hund's Rule -Developed by the German scientist, -A rule of thumb stating that subshells fill so that the number of unpaired spins is maximized. Also known as therule of maximum multiplicity. - Electrons are added to the lowest available energylevel (shell) of an atom.
Pauli Exclusion Principle -it was formulated by the Austrian-born physicist Wolfgang Pauli in 1925. -ThePauli exclusion principle states thateachelectron must have its own uniqueset of quantum numbers that specify its energy. -no two electrons can occupy the same quantum state at the same place and time
Atoms are made up of 3 types of particles electrons , protons and neutrons . These particles have different properties.
Electrons: tiny, very light particles that have a negative electrical charge (-)
Protons: much larger and heavier than electrons and have the opposite charge, protons have a positive charge
Neutrons: large and heavy like protons, however neutrons have no electrical charge
Centrifugal Force
-forcethatmakesobjectsmoveoutwardswhentheyarespinning around somethingortravellinginacurve.
-The protons and electrons stay together because just like two magnets, the opposite electrical charges attract each other.
What keeps the protons and electrons from crashing into each other?
-The electron spins around nucleus(the center of the atom). The centrifugal force of the spinning electron keeps the two particles from coming into contact with each other.
Electron Cloud
-Atoms are extremely small. One hydrogen atom, for example, is approximately 5 x 10-8 mm in diameter.
- Protons and neutrons behave like small particles, sort of like tiny billiard balls.
- The electron has some of the properties of a wave. In other words, the electron is more similar to a beam of light than it is to a billiard ball.
- Thus to represent it as a small particle spinning around a nucleus is slightly misleading. In actuality, the electron is a wave that surrounds the nucleus of an atom like a cloud.
Hydrogen: a proton surrounded by an electron cloud
Neutron
-Helium has the 2 protons in the nucleus have the same charge on them.
-They would tend to repel each other, and the nucleus would fall apart.
-To keep the nucleus from pushing apart, helium has two neutrons in its nucleus.
-Neutrons have no electrical charge on them and act as a sort of nuclear glue, holding the protons, and thus the nucleus, together.
Ion
- An atom that carries an electrical charge
- total number of electrons is not equal to the total number of protons
● cation : -positively charged ion
-has fewer electrons than protons
● anion : -negatively charged ion
- has more electrons than protons
Listed below are three forms of hydrogen; 2 ions and the electrically neutral form.
H+ : a positively charged hydrogen ion
H : the hydrogen atom
H- : a negatively charged hydrogen ion
Isotope
- two atoms with same number of protons but different number of neutrons
- their chemical properties are almost identical since the chemical behavior of an atom is largely determined by its electronic structure.
Democritus:-in 300B.C, was the first to theorize the existence of atoms
Aristotle however disagreed with Democritus and believed that atoms were made from the 4 elements; earth, air, fire, and water Lavoisier (late 1700's)-stated earliest version of both the Law of Conservation of mass and discovered combustion Proust (1799)- Proust believed that if a compound were to be broken down, it would still contain the same ratios as in the compound; continued on with Lavoisier and proved the law of definite porportions Dalton (early 1800's)- all matter is made of atoms -all atoms of given element are the same -atoms of one element can combine with another to form chemical compounds -a chemical reaction is a rearrangement of atoms J.J. Thompson (1850)- proved existence of electrons; uses the plum pudding model Rutherford (1905)- showed atoms had dense centres and electrons outside of them -suggested atoms are mostly empty space; proved Thompson's model to be incorrect Niels Bohr (1885-1962)- studied gaseous samples of atoms -proposed that electrons surrounds the nucleus in shells -when exciting electrons of a certain element, it gives off light
All these people contributed to the model of the atom. However, the atom today consists of 3 subatomic particles: protons, electrons, neutrons. Protons and neutrons lies within a dense nucleus whilst the electrons surround the nucleus in shells.
Sometimes in a chemical process, not all the products are used up. Percent yield is there to help us calculate the % of the product recovered.
% Yield = .grams of actual product recoveredX 100%
grams of product expected from stoichiometry
The percent yield should never be higher than 100%. Where did all that extra stuff come from anyway?
Let’s do an example:
Consider this equation: 1 CrCl2 + 2 Ca à 2 CaCl + 1 Cr
If 15.0g of CrCl2 is reacted with excess Ca and 4.10g of Cr was produced, what is the % yield?
STEP 1: Check to see if the equation is balanced. If not, balance it.
It is balanced in this case.
STEP 2: Find the amount of Cr produced when 15.0g of CrCl2 reacts
15.0g CrCl2 X 1mol CrCl2= 0.12195mol CrCl2ßconvert to moles
123g CrCl2
0.12195mol CrCl2 X1mol Cr .= 0.12195mol Crßuse mole ratio
1mol CrCl2
0.12195mol CrX 52.0g Cr = 6.34g Crßconvert to grams
1mol Cr
STEP 3: Find % yield
% yield =4.10g Cr obtained . X 100%= 64.7% yield
6.34g Cr expected
For every 100.0g of product predicted, only 64.7g of product is actually formed.
PERCENT PURITY
Sometimes the reactants that were used are not pure, meaning there are bits of other elements in the main element. % purity calculates how much is actually there.
% Purity =mass of pure substance X 100%
mass of impure sample
Again, the % purity should never go above 100%.
Let’s start with an easy example:
If a 10.0g sample of zinc ore contains 7.3g of zinc metal, what is the percent purity?
Find the percent purity
% Purity =7.3g Zn metal (pure substance) X 100%= 73.0% purity
10.0g Zn ore (impure sample)
Here’s a harder example:
Consider this equation: Ca + H2O à CaOH + H2
If 6.2g of impure calcium, that is 82% pure, is reacted, how many moles of hydrogen gas is produced?
STEP 1: balance the equation
2 Ca + 2 H2O à 2 CaOH + 1 H2
STEP 2: calculate the mass of Ca
% Purity X mass of impure Ca = mass of pure Ca
82.0% X 6.2g impure Ca= 5.084g pure Ca
100%
STEP 3: calculate moles of H2 produced by 5.1g Ca
5.1g Ca X 1mol Ca =0.1268mol Caßconvert to moles
40.1g Ca
0.1268mol Ca X 1mol H2= 0.063mol H2ßuse mole ratio
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