chem sem 1

sig fig rules

1. Any non- zero number is significant 

2. Zero values that are sandwiched between nonzero digits are significant, they always count 

3. Zeros appearing in front of the non -zero digits are not significant 

4. Zeros at the end of number and to the right of the decimal point are significant 

5. Trailing zeros are significant only if a decimal point is shown 

MULTIPLICATION/DIVISION: round to fewest # of sig figs

ADDITION/SUBTRACTION: round to fewest decimal places (least precise)

percent error formula

(measurement- target value)

—- — — — — — — — — — x100

(target value)

physical change

 A change in the physical properties of matter, occurs without changing the identity of a substance 

physical property

 a process where a substance that can be observed or measured with out changing its chemical identity 

chemical change

A chemical reaction, one substance changes into another substance 

chemical property

a characteristics of a substance that can only be observed when the substance undergoes change 

mixture

A mixture is made of two or more different substances that are combined.  The substances are not chemically bonded which means a mixture can be separated into its original parts. A mixture is made up of more than one element or compounds

homogeneous mixture

 type of mixture where the solution in uniformed throughout  sugar dissolves in water) - CANNOT BE SEPARATED BY PHYSICAL MEANS 

heterogeneous mixture

A mixture whose components have an uneven distribution

pure substance

made of only one type of atom or one type of molecule, Made up of one element and one compound. Cannot be physically separated into different kinds of matter

compound

 A compound is a molecule that can contain at least two different elements that are chemically combined into a fixed ratio. 

filtiration

Filtration separates an insoluble solid (one that does not dissolve) from a liquid or solution.Used to separate heterogeneous mixtures composed of solids and liquids.

chromatography

Chromatography is a separation process that requires two different phases of matter.

It can be used to separate two solids that are mixed to create the same liquid.

Separates components of a mixture based on the ability of each component to be drawn across the surface of another material.

The mixture is usually liquid and is drawn across chromatography paper.

Separation occurs because various components travel at different rates.

The component with the strongest attraction for paper will travel the slowest.

evaporation

Evaporation separates a soluble solid (one that does dissolve) from a liquid, usually water.

The solution of the solid and liquid is boiled until the liquid evaporates into the air.

The salt is left behind in its original form.

extraction

Extraction is a method of isolating one compound from another.

The mixture is brought into contact with a solution in which the substance wanted is soluble (will dissolve), but the other substances present are insoluble (won’t dissolve).

distillation

Distillation is the action of purifying a liquid by the process of heating and cooling.

It can be used to separate two liquids that have different boiling points.

By heating them to evaporate one and then cooling it to condense it, while the other remains a liquid.

This method is mostly used to purify liquids.

Used to separate homogeneous mixtures based on differences in boiling points of substances involved.

crystallization

A separating technique that results in the formation of pure solid particles from a solution containing a dissolved substance.

Produces a highly pure solid.

As one of the substances evaporates, the dissolved substance comes out of the solution and collects as crystals.

centrifugation

Rotates containers or liquid to separate suspended materials with different densities.

magnet

Can be used to separate a magnetic substance from a non-magnetic substance.

decantation

It is done to separate particles from a liquid by allowing the solids to settle to the bottom of the mixture and pouring off the particle-free part of the liquid.

A physical separating technique that separates components of a mixture by allowing them to settle and then carefully pouring off the liquid or lighter component, leaving the solid or heavier component behind.

electrolysis

The decomposition of a liquid by passing an electric current through it.

Must have: 

• an electrolyte and the liquid that the electric current flows through

• a negative electrode (the anode)

• a positive electrode (the cathode)

Democritus theory

Matter is made of tiny, indivisible particles called Atoms 

Atoms cannot be created or destroyed 

Key idea: Matter is made of particles 

John Dalton

Atoms of the same element are identical 

Different elements have different atoms 

Atoms combine in whole - number ratios to form compound 

Key Idea: First scientific atomic theory  

J.J Thomson

Discover the electron 

Plum pudding Model 

Key idea: Atoms are divisible and contain smaller particles 

Rutherford

Gold foil experiment shows that the atom is mostly empty space 

Discovered the nucleus (dense, positive center) 

Key idea: Atom has a small dense nucleus 

Bohr

 Electrons moved in fixed energy levels around the nucleus 

Electrons jump between levels by gaining or losing energy 

Key idea: Energy levels are quantized

What are the charges of the 3 subatomic particles and where are they located?

Protons - Protons have a charge of +1 and live in Nucleus, they have a mass of 1 

Neutrons- Neutrons have a charge of 0 and live in the Nucleus, they have a mass of 1. 

Electrons- Electrons have a charge of -1 and live in the Electron cloud (the rings around the Nucleus), they have a mass of 0  

How to find # of subatomic particles, atomic number, mass number

Mass number = Protons + Neutrons 

Protons = Atomic Number 

Neutrons = Mass Number - Atomic Number (Neutrons are never on the periodic table) 

Electrons = Protons (Losing and electron makes a positive ion, Gaining electrons makes a negative ion) 

cation

loses electrons (+)

Anion

atoms gain electrons (-)

Isotopes

atoms of the same element that have different numbers of neutrons but the same number of protons giving them a different mass number. 

How to write isotopic notation

¹²⁷ ₅₃I

The top number is the MASS of the isotope and the bottom number is the atomic number. 

Since the atomic number is equal to the number of protons we know that there are 53 protons and since protons and neutrons make up the mass if you subtract the mass by 53 you will get the number of protons. 

How to find average atomic mass

1. convert % natural abundance to decimals

2. multiply abundance to mass

3. add results of all isotopes

 

aufbau order

The Aufbau principle states that electrons occupy the lowest  energy orbitals available before filling higher - energy ones (1s² 2s² 2p⁶) 

1s→2s→2p→3s→3p→4s→3d→4p→5s→4d→5p→6s→4f→5d→6p→7s→5f→6d→7p

Pauli exclusion principle

Same orbital, Different spin: If two electrons share the same orbital they must have different spins ( one up and one down) to have different sets of numbers 

Hunds rule

For a given electrons subshell, electrons will first occupy each orbits singly with parallel spins (same direction) before any paring occurs, maximizing the total spring and leading to the lowest energy state for the atom - Think of it like filling sets on a bus you take separate seats before sitting next to someone. 

what are the different groups of the periodic table?

Group 1 - Alkali metals (Li, Na, KI, Rb, Cs) 

Key Properties - 1 Valence electron, very reactive, metal

Group 2 - Alkaline Earth Metals (Be, Mg, Ca, Sr, Ba) 

Key Properties - 2 valence electrons, reactive but less reactive than group 1, Forms +2 ion, harder and denser than alkali metals 

Group 3 - 12 - Transition metals 

Kep Properties - Good conductor of heat and electricity, multiple states, less reactive that Groups 1-2 

Group 17- Halogens (F, Cl, Br, I ) 

Key properties - 7 valence electrons, very reactive non metals, form - 1 ions

Group 18- Noble Gases (He, Ne, Ar, Kr, Xe) 

Key Properties- full valance shell unreactive, is a gas, does not form ions easily (Helium has 2 valence electrons) 

what are the periodic tabel trends?

[insert photo]

Atomic Radius - half the distance from the nucleus to the outermost electron shell. 

Trend: 

Increases down a group 

Decreases across a period 

Why? 

Down a group: more electron shells 

Across a period: greater nuclear charge pulls electrons closer 

Ionic Radius - The distance from an ions nucleus to its outer most shell 

Trend: 

Increases down a group 

Decreases across a period 

Ionization Energy- energy required to remove a valence electron

Trend

Decreases down a group 

Increases across a period 

Metals have low ionization energy

Nonmentals have high ionization energy 

Electronegativity - ability of an atom to attract electrons in a bond 

Trend 

Decreases down a group 

Increases across a period  

Fluorine is the most electronegative element 

Electron Affinity - Energy change when an atom gains an electron 

Halogens have high electron affinity 

Noble gases  have very low or zero electron affinity  

Atoms close to a full valence shell strongly attract electrons (groups 1 and 2 will have low electron affinity because they are the furthest away from getting a complete shell) 

Effective nuclear charge

Effective nuclear charge (Zeff) is the net positive charge felt by valence electrons after accounting for shielding by inner electrons The formula: Z_eff= Z-S 

Z = Atomic number (number of protons) 

S = Shielding Constant (Number of inner/ core electrons) (Shielding Constant = non-valenced 

electrons) 

How to calculate Z_eff 

Step 1: write the electron configuration 

Step 2: identify valence electrons 

Step 3: Count non valence electrons 

Step 4: Subtract 

polar vs non polar covalent bonds?

Nonpolar Covalent 

• Electrons are shared equally 

• Similar electronegatives 

Polar Covalent 

• Electrons shared unequally

properties of covalent compounds

• Low metaling and boiling points 

• Poor electrical conductivity 

• Often gasses or liquid 

• Directional bonds (specific shapes)  

properties of metallic bonds

• Electrons can easily move to carry charge or heat 

• Malleable and ductility 

• Reflect light  

properties of ionic compounds

• HIgh melting and boiling points 

• Hard brittle crystals 

• Conduct electricity when dissolved 

• From crystal lattices 

London Dispersion Forces

Present in all molecules due to temporary electron shifts; strongest in large, nonpolar molecules. 

Dipole-Dipole Interactions

Attractions between permanent positive and negative ends of polar molecules.

Hydrogen Bonding

A very strong dipole-dipole force between H (bonded to N, O, F) and an N, O, or F on another molecule. 

Ion-Dipole/Ionic Forces

 Strongest IMFs, occurring between ions and polar molecules (like salt in water) or between ionic compounds.