NY Chemistry Regents - August 2024

Dalton’s Model

Atoms are hard indivisible spheres of different sizes | Matter is conserved during a chemical reaction

Thompson’s Model

Atoms have small, negatively charged particles as part of their internal structure | Cathode rays are deflected by magnetic/ electric fields

Rutherford’s Model

An atom is mostly empty space with a small, dense positively as part of their nucleus, electrons go around the nucleus | Most alpha particles pass straight through gold foil but a few are deflected.

Bohr’s Model

Packets of energy are absorbed or emitted by atoms when an electron changes shells, electrons revolve around the nucleus in concentric orbits | Unique spectral lines are emitted by excited gaseous elements.

Orbital Model (modern model)

Electron Cloud Model. Electrons located in ORBITALS which is the most probable location of an electron.

Rutherford’s Gold Foil Experiment

When he bombarded the foil, most of the particles (alpha particles which are positively charged) went straight through the foil, BUT, some of the particles bounced back. Two very important results were concluded by this experiment. 1. An atom is made up of mostly empty space 2. An atom has a nucleus that is positively charged.

Fission

Type of artificial transmutation. A neutron bombards an atom causing it to split into two or more pieces and gives off a lot of energy. This is the energy behind nuclear power plants (controlled chain reaction) and atomic bombs (uncontrolled chain reaction).

Fusion

two nuclei unite to form a heavier nucleus (“u”- unit). High temperature and pressure are needed, which is why this occurs on the SUN. Fusion creates more energy than fission.

Alpha Particle

weakest penetrating power | HEAVIEST

Gamma Radiation

strongest penetrating power | LIGHTEST

Tracers

Carbon-14 – Date LIVING THINGS

Uranium-238 & Lead 206 – Date NON-LIVING THINGS

MEDICAL Technetium-99

brain tumors

MEDICAL Iodine-131

thyroid disorders

MEDICAL Radium & Cobalt-60

treatment of cancer

If q is negative

exothermic reaction (release heat)

If q is positive

endothermic reaction (absorb heat)

Heat flows from

an area of higher temperature to an area of lower temperature until both temperatures are the same

Heat diagram

slants = state of matter | plateau’s = phase change

Ideal Gas Laws

1. A gas is composed of particles that are in continuous, random, straight line motion.

2. There is a transfer of energy between colliding particles; the total energy remains constant.

3. The volume of gas particles is negligible in comparison with the volume of space they are in. There is a lot of space between the particles.

4. Gas particles are considered as having no force of attraction for each other.

IONIZATION ENERGY

The amount of energy needed to remove an electron. The smaller the amount of ionization energy, the easier it is to lose an electron.

ELECTONEGATIVITY

The attraction for electrons; the larger the electronegativity, the more the atom attracts electrons.

COMBUSTION REACTIONS

the reaction of a carbon-based compound with oxygen; the products are carbon dioxide and water (first 6 reactions on Table I)

CLASSIFYING CHEMICAL REACTIONS

When two or more chemicals are brought together, a chemical change (reaction) is likely to take place. Some evidence that a chemical reaction has occurred include the following

1. A color change occurs

2. A solid forms (precipitate) – INSOLUBLE (Table F)

3. A gas is released (bubbles form)

4. Heat and/or a flame are produced (exothermic)

5. Heat is absorbed (endothermic)

Collision Theory

in order for a chemical reaction to occur, effective collision of molecules must occur. Both the energy of the collision and the angle of the collision are important. The more collisions, the faster the rate of reaction.

• Concentration: an increase will increase rate of reaction

• Temperature: an increase will increase rate of reaction

• Surface area: increasing SA will increase rate of reaction

• Nature of compound: Ionic will react faster than covalent

• Catalyst: increases rate of reaction by decreasing activation energy which is the energy required for a reaction to start.

Potential Energy Diagram (Endo vs. Exo)

enDo comes before eXo because d is before x in the alphabet thus endo reactions finish above the start and vise versa

pH Scale

• Every step on the pH scale is 10x - Going from a pH of 3 to 4 means the H+ concentration decreases 10x - Going from as pH of 5 to 3 means the H+ concentration increases 100x

Oxidation

The loss of electrons by a molecule, atom, or ion.

Reduction

The gain of electrons by a molecule, atom, or ion.

RULES FOR ASSIGNING OXIDATION NUMBERS

1. Free elements (not combined with any other element) have an oxidation number of zero. Ex: Na, O2, H2

2. All metals in Group 1 have an oxidation number of +1.

3. All metals in Group 2 have an oxidation number of +2.

4. F (fluorine) always has an oxidation of _1.

5. The oxidation of simple ions is equal to the charge on the ion. Ex: Mg+2 has an oxidation number of +2.

6. The sum of the oxidation numbers must equal 0. Examples: sodium chloride: Na+1 + Cl-1 = NaCl (sum of the oxidation numbers equals 0); magnesium chloride: Mg+2 + Cl-1= MgCl2 (sum of the oxidation numbers equals 0).

7. In ions (charged particles), the sum of the oxidation numbers of all the atoms must equal the charge of the ion. Example: sulfate ion SO4-2 . O has an oxidation number of 2, and therefore (2) x (4) = 8. Remember that the overall charge of this ion has to be 2, so what must the oxidation number of S be?

8. Oxygen has an oxidation number of 2 in all its compounds except in peroxides (Ex: H2O2), when oxygen has an oxidation number of 1, and in compounds with F (Ex OF2), when oxygen has an oxidation number of +2.

9. Hydrogen has an oxidation number of +1 in all compounds combined with a nonmetal. The exception is in metal hydrides (metal and hydrogen, LiH, and CaH2), when hydrogen has an oxidation number of _1.

Voltaic Cell

• Spontaneous - Converts chemical to electrical energy Anode is always the site of oxidation (in voltaic cell it is negatively charged)

• Cathode is always the site of reduction (in voltaic cell it is positively charged)

• Two half-cells each with an electrode (metal strip)

• The half-cell with the metal that is more reactive (Table J) will be the anode, and will therefore be oxidized.

• Wire is to allow the electrons to travel.

• Salt bridge allows ions to travel freely between the two half-cells.

Electrolytic Cell

• Non-spontaneous - converts electrical energy to chemical energy

• Requires an energy source (battery)

• Anode is the site of oxidation: the charge is positive

• Cathode is the site of reduction: the charge is negative.