Elements, Compounds and Mixtures and Their Properties
Elements can not be broken down by chemical change. Symbols of elements can be found on the Periodic Table. Names of elements can be found on Table S. Example: Mg, Fe, oxygen, copper.
Compounds are made from two or more elements in fixed proportions. Example: H2O, CH4.
Atomic Theories, Atoms and Ions
3. Protons (+1charge) and neutrons (neutral) are located inside the nucleus. Electrons (-1 charge) are located outside the nucleus.
4. Gold foil experiment led to the following conclusions: most of the atom is empty space, inside an atom there is a small, dense, positively charged nucleus.
5. An orbital is defined as a region of the most probable electron location according to the wave-mechanical model of an atom.
6. All atoms of an element MUST have the same number of protons, which is equal to the atomic number.
7. The mass of an atom is equal to the sum of protons and neutrons.
8. Isotopes are atoms of the same element (same atomic number which means same number of protons) that have different mass (different number of neutrons).
9. The electron configuration of an atom of each element in a ground state can be found on the Periodic Table. In an excited state, one electron jumps from a lower to a higher energy level. For example, instead of 2-8-2, we would see 2-7-3 (an electron jumped from the second to the third energy level).
10. In a neutral atom, the number of protons and electrons is equal.
Formulas, Equations and Chemical Reactions
11. In a synthesis reaction two or more molecules come together to form one bigger molecule: A+B--> AB
12. Decomposition is the opposite of synthesis: AB --> A+B
13. In a single replacement reaction, one element replaces another: A +BC --> B +AC
14. In a double replacement reaction partners get exchanged: AB +CD --> AD +CB
Chemical Calculations
15. According to the conservation of mass, mass of the reactants must be equal to the mass of products. Same applies to charge.
16. An empirical formula is a formula with the simplest ratio of atoms. This means the subscripts in the formula can not be divided any further. For example in C2H4, we can divide both subscripts by 2 to get CH2.
17. Table T on the Reference Table shows the formula for mole calculations. Number of moles = given mass/ gram-formula mass.
18. The coefficients in the equation represent moles. For example 2A+B --> 3C How many moles of A are needed to react to make 6 moles of C? The mole ratio of A to C is 2 to 3 (from the coefficients). To make 6 moles of C, we will need 2*2=4 moles of A
Energy and Heat
Temperature is the measure of the average kinetic energy.
All of the heat equations can be found on Table T in the Reference Table.
q = mHf where q=heat, m is mass and Hf =heat of fusion. This equation is used when solid is melting or liquid is freezing. Hf for water can be found in Table B.
q=mCΔT where q=heat m = mass and C = specific heat capacity. This equation is used when there is a change in temperature. C for water can be found in Table B.
q = mHv where q=heat, m is mass and Hv =heat of vaporization. This equation is used when something is vaporizing. Hv for water can be found in Table B.
The difference between potential energy of products and potential energy of reactants is equal to the heat of reaction.
Gases
When temperature, pressure, and volume is equal for two gases, the number of moles and atoms are equal as well.
Kinetic molecular theory has the following statements which need to be memorized:
Gas particles have negligible volume.
The gas particles are in continuous random motion and move in straight lines.
No forces of attraction or repulsion are considered to exist between the particles.
Collisions of gas particles may transfer energy from one particle to another, but the total kinetic energy remains the same.
A sample of gas behaves MOST like an ideal gas under high temperature and low pressure.
Nuclear Chemistry
Table N on the Reference Table shows different isotopes with their decay modes and half lives.
Table O lists nuclear particles with their respective symbols. The numbers on the top are mass numbers and the bottom ones are atomic numbers.
Gamma rays have the greatest penetrating power, but the least ionizing power.
Alpha rays have lowest penetrating power and higher ionizing power.
Nuclear reaction such as fission and fusion convert mass into energy. These reactions produce much more energy than chemical reactions.
Radioactive Isotopes Uses
Iodine-131 = treatment of thyroid disorders
Iodine-123 = detection of thyroid disorders
Carbon-14 = used as a tracer, to follow the course of a chemical reaction. It is also used for dating lining materials (figuring out the age of wood, bone etc)
Cobalt-60 = sterilizing medical equipment
Uranium-238 = geological dating (figuring out the age of rocks)
Transmutation is the conversion of one element into another
Fusion: light nuclei come together to form a heavier nucleus.
Example:
Fission: bombardment of a large atom such as uranium with a neutron.
Example:
Periodic Trends
Ionization energy and electronegativity increase as we go from the left to the right across a Period on the Periodic Table.
Metals are to the left of the staircase on the Periodic Table. Nonmetals are to the right of the staircase on the Periodic Table. Metalloids are on the staircase and include: B, Si, Ge, As, Sb, Te.
Use Table S to find electronegativity, atomic radius, density, melting and boiling points of all elements. You can also use it to determine periodic trends if you forgot them.
Two elements have similar chemical properties if they are in the same Group (column) on the Periodic Table because they have the same number of valence electrons.
Electronegativity is a scale for the attraction of an element for electrons in a chemical bond.
The elements on the Periodic Table of the Elements are arranged in order of increasing atomic number.
Chemical Bonding
The stronger the intermolecular forces, the higher the boiling point of a substance.
A nonpolar covalent bond is a bond where electrons are equally shared. In a polar covalent bond, electrons are shared unequally.
The most polar bond results from the biggest electronegativity difference. Table S on the reference table lists all the elements and their electronegativity values.
Solutions
Table T provides formulas for calculating concentrations including molarity and parts per million.
When a compound dissolves in water (or any other pure solvent), it increases the boiling point of water (or that pure solvent) and decreases its freezing point.
The formula for dilution is M1V1= M2V2 where M stands for molarity and V for volume.
Table F on the Reference Table is a solubility table. A compound that is soluble will dissolve in water.
Kinetics and Equilibrium
Energy is absorbed when a bond is broken and energy is released when a bond is formed.
Kinetic molecular theory has the following statements which need to be memorized:
Gas particles have negligible volume.
The gas particles are in continuous random motion and move in straight lines.
No forces of attraction or repulsion are considered to exist between the particles.
Collisions of gas particles may transfer energy from one particle to another, but the total kinetic energy remains the same.
In order for reactant molecules to collide effectively and product products, they need to have proper orientation and energy.
At equilibrium the rates of forward and reverse reactions are equal and the concentrations of reactants and products are constant.
A catalyst is a substance that increases the rate of the reaction by lowering the activation energy by providing an alternative reaction pathway.
Systems in nature tend to undergo changes toward lower energy and higher disorder.
Temperature is the measure of the average kinetic energy of the particles
Heat always flows from the hotter to the cooler object.
Table I on the Reference Table gives the net amount of heat released or absorbed by different reactions.
Acids and Bases
According to the Bronsted Lowry acid-base theory, acid is a proton (H+) donor and base is a proton acceptor.
A reaction between an Arrhenius acid and base always produces water and salt. This reaction is called neutralization.
Table L on the Reference Table lists common bases. Table K lists common acids.
An electrolyte is a substance that can conduct electricity when dissolved in water. The higher the pH the more basic solution is and the more OH- ions it has. The lower the pH the more acidic solution is and the more H+ ions it has.
Electrochemistry
An Ox ( anode is oxidation) and Red Cat ( reduction occurs at the cathode).
Electrolytic cell requires an input of energy to operate. It converts electrical energy into chemical energy. Voltaic cell is the opposite. In Voltaic cell, chemical energy is converted into electrical energy.
A voltaic cell has spontaneous reactions, while an electrochemical cell has nonspontaneous reactions.
OIL RIG. OIL (oxidation is loss of electrons). RIG (reduction is gain of electrons).
Laboratory
Distillation is a laboratory technique used to separate two liquids based on their boiling points.
Titration is a laboratory technique used to identify the concentration of an unknown acid or base.
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