Chemistry: Principles of Chemistry - Unit 1

processes responsible regarding, solid and gas

• sublimation (solid to gas)

• deposition (gas to solid)

diffusion

• it is the overall movement of particles from an area of high concentration to an area of low concentration

• a gas will diffuse through all the space it can find

• if you spray some perfume in one corner of the room, soon you will be able to feel the smell at the other end of the room

solubility curve

it is a curve that shows how the solubility of a substance (in grams per 100g of water) changes with temperature

outline the main assumptions of the kinetic theory of matter

• matter is made up of atoms, molecules and ions of different sizes

• at the same temperature, small particles move faster than large particles

• as temperature rises, the particles have more kinetic energy and move faster

• solids are made up of ordered arrangement of closely packed particles

• liquids do not have particles arranged regularly, particles can move around

• in gases, the particles are far apart, they move fast, their motion is random

centrifuging

• it is method for separating out particles of different densities in a substance

• it can be used to separate suspended solids (very small particles of solid) from the liquid they are suspended in

• it is used when the particles are so small that they can’t be separated via filtration

• in a centrifuge, the sample is spun at high rates, the forces the solid particles to settle down at the bottom of the tube, the liquid can be decanted

atom

this is the smallest particles of a chemical element that can exist

element

this is a substance made up of only one type of atom

how are the element listed and approximately how many are there

• they are listed in the periodic table

• there are approximately 100

• elements are classified into two groups based on their properties: metals and non-metals

compounds

• this is the new product of when elements combine through chemical reactions

• two or more elements combined chemically in fixed proportions which can be represented by formulae

mixture

• this consists of two or more elements or compounds not chemically combined together

• the constituent materials keep their own chemical properties, btu the mixture may have

Methods through which mixtures can be separated (there are five). Do these involve chemical reactions?

• Filtration

• evaporation/crystallization

• simple distillation

• fractional distillation

• chromatography

• they do not involve chemical reactions

Simple distillation

• This is used to separate liquid from a solution - the liquid boils off and condenses in the condenser

• The thermometer will read the boiling the boiling point of the pure liquid.

• contrary to evaporation, we get to keep the liquid (it drips and is collected into a separate beaker).

Crystallization/Evaporation

• Evaporation is a technique for separation pf a solid dissolved in a solvent from a solvent (e.g. salt from H₂O).

  • The solution is heated until all the solvent evaporates; the solids stays in the vessel.

• Crystallization is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved).

  • then, we cool down the solution.

  • as we do it, the solid starts to crystallize, as it becomes less soluble at lower temperatures.

  • the crystals can be collected and separated from solvent via filtration.

Fractional distillation

• this is a technique for separation of a mixture of liquids.

• it works when liquids have different boiling points.

• The apparatus is similar to the one of simple distillation apparatus, with the additional fractioning column placed on top of the heated flask.

• The fractioning column contains glass beads.

• it helps to separate the compounds.

• in industry, mixtures are repeatedly condensed and vaporized.

• The column is hot at the bottom and cold at the top.

• the liquids will condense at different heights of the column.

Filtration

• This is used to separate an insoluble solid suspended in a liquid.

• the insoluble solid (called a residue) gets caught in a filter paper, because the particles are too big to fit through the holes in the paper.

• the filtrate is the substance (liquid) that comes through the filter paper.

• Apparatus: filter paper + funnel.

Chromatography

• This is used to separate a mixture of a substance dissolved in a solvent.

• in a paper chromatography, we place a piece of paper with a spot containing a mixture in a breaker with some solvent.

• The bottom of the paper has to be in contact with the solvent.

• The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).

Paper Chromatography Experiment

• A start line is drawn near the bottom of the paper. the mixture is spotted on the line

• A beaker is filled with small amount of solvent (it cannot touch or go above the start line when paper is placed in a beaker)

• Paper is hung on a rod and placed in a breaker.

• Solvent travels up the paper, thus separating the components.

• Before Solvent level reaches the end, the paper is taken out and the finish line is marked. The paper is dried.

• The procedure works when the components dissolve differently in the solvent. more soluble components travel further up the paper. Less soluble components have a stronger attraction for the paper and travel less slowly with the solvent, therefore less further up the paper.

• Paper is called the stationary phase - it doesn’t move. Solvent is the mobile phase.

How is R_f Calculated?

Distance moved by the spot (solute component) / distance moved by solvent

In a paper chromatography experiment, a compound A was found to have an R_f value of 0.85 - what does it tell you about the compound?

it has a higher affinity for the solvent than for the paper.

Separating funnel

• This is an apparatus for separating immiscible liquids.

• two immiscible liquids of different densities will form two distinct layers in the separatory funnel.

• we can run off the bottom layer (the liquid with greater density) to a separate vessel.

Plum-pudding model

• the atom is a ball of positive charge with negative electrons embedded in it.

Bohr/Nuclear model

• The nuclear model suggets that electrons orbit the nucleus in energy levels (at specific distances from nucleus).

• it came about the alpha scattering experiments conducted by Ernest Rutherford and two students.

Later experiments led to the discovery of smaller, positive particles in the nucleus

• These particles are called protons

Work of James Chadwick provide evidence for?

• the existence of neutrons in the nucleus.

Structure of an atom

• The atom has a small central nucleus ( made up of protons and neutrons ) around which there are electrons.

State the relative masses and relative charges of the proton, neutron and electron

• Masses: 1, 1, very small (respectively)

• Charges: 1, 0, -1 (respectively)

Why atoms are electrically neutral

• They have the same number of electrons and protons

Radius of an atom

• 0.1 nm

Radius of a nucleus and what is it compared to that of the atom

• 1 × 10^-14m and less than 1/10000 of the radius of the atom

What name is given to the number of protons in the nucleus?

• Atomic number

Atoms of the same element have the same number of which particle in the nucleus?

• protons

Where is the majority of mass of an atom

• The nucleus

Mass number

• The total number of protons and neutrons in the nucleus.

How does one calculate the number of neutrons using mass number and atomic number?

• Subtract the atomic number from the mass number.

What is an Isotope? Do isotopes of a certain element have the same chemical properties?

• Atoms of he same element (same proton number) that have a different number of neutrons.

• They have the same chemical properties as they have the same electronic structure.

Relative atomic mass

• The average mass value of one atom (taking into account the abundance of isotopes), compared to 1/12 of the mass of one carbon-12 atom.

He, Be, F, Na, Ca, configurations (respectively)

2

2,2

2,7

2,8,1

2,8,8,2

Describe the properties of noble gases. Discuss the trends in properties down the group.

• Non-metals, Colorless gases at room temperature, low boiling points, unreactive (full outer shell; they don’t easily accept or lose electrons).

• The boiling point increases down the group, as the atoms get heavier.

Explain: Solute, solvent, solution, miscible, immiscible, soluble, insoluble.

• A solute is a substance that is dissolved in a solvent. Together they form a solution.

• Miscible refers to the substances (particularly liquids) that mix together in all proportions, e.g. water and alcohol. Water and oil are immiscible, i.e. they do not mix.

• Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in water. An insoluble substance won’t dissolve in a particular solvent.

Columns of the periodic table are called?

• Groups

Rows of the periodic table are called?

• Periods

Are elements in the same group similar or different?

• they may have similar chemical properties, as they have the same number of outer shell electrons

In terms of energy levels, what are the differences between elements of the same period?

• they have the same number of energy levels

Electrons occupy particular energy levels, with each electron in an atom at a particular energy level; which available energy level do electrons occupy?

• The lowest available energy level

The elements of group 0 are more known as?

• The noble gases

What makes the periodic table periodic?

• Similar properties of elements occur at regular intervals

Elements in the same group have the same number of electrons in their outer shell; what does this tell us about their chemical properties?

• they have similar chemical properties

In terms of shells, what is the difference between elements in the same period?

• They have the same number of shells

Shat change in shell number is seen as one moves down a group?

• the number of shells increases

Early periodic tables were incomplete and elements were placed in inappropriate groups if what was to be followed?

• The strict order of atomic weights

Knowledge of what made it possible to explain why the order based on atomic weights was not always correct?

Isotopes

Mendeleev overcame some problems with the table by doing what? He also changed the order of some elements based on what?

• Leaving gaps

• Atomic weights

The majority of elements are?

• Metals

Elements that react to form positive ions are?

• Metals

Elements that do not form positive ions are?

• Non-metals

Elements in Group 1 are known as?

• The alkali metals

Elements in Group 7 are known as?

• The halogens

Ionic bonding

• This is the transfer of electron(s) from a metal atom to a non--metal atom to form positive and negative ions.

• There is a relatively strong electrostatic attraction between the positive and negative ions which is called an ionic bond.

Ionic compound

• They are held together in a giant lattice.

• It’s a regular structure that extends in all directions in a substance.

• Electrostatic attraction between positive and negative ions holds the structure together

State Properties of ionic substances

• High melting and boiling point (strong electrostatic forces between oppositely charged ions).

• Do not conduct electricity when solid (ions in fixed positions).

• conduct when molten or dissolved in water - ions are free to move.

5 examples of positive ions and 5 examples of negative ions. What is important when working out a formula of an ionic compound?

• E.G. Positive: Na⁺, Mg²⁺, Al³⁺, Ca²⁺, Rb⁺

• E.G. Negative: Cl^-, Br^-, SO₄^2-, NO₃^-, OH^- (Chloride, bromide, sulfate, nitrate, hydroxide).

• Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other.

How are ionic compounds formed? (in terms of MgO case)

• Reaction of a metal with a non-metal.

• Electron transfer occurs - metal gives away its outer shell electrons to non-metal

• Mg is in group II, so it has 2 available outer shell electrons

• O is in group VI, so can accept 2 electrons to get a full outer shell configuration

• Mg becoms Mg²⁺ and O becomes O^2- (oxide)

Covalent bond

• This is a shared pair of electrons between two atoms

Describe the structure and properties of simple molecular covalent substances

• Do not conduct electricity (no ions)

• small molecules

• weak intermolecular forces

• Low melting and boiling points

How do intermolecular forces change as the mass/size of the molecule increases?

• they increase.

• That causes melting/boiling points to increase as well (more energy needed to overcome these forces).

What are giant covalent substances

• solids, atoms covalently bonded together in a giant lattice.

• high melting/boiling points - strong covalent bonds.

• mostly don’t conduct electricity (no delocalised e^-)

• Diamond, graphite, silicon dioxide (silica).

Properties of allotropes of carbon

Metallic Bonding

• Forces of attraction between delocalized electrons and nuclei of metal ions

Properties of metals

• High melting/ boiling points (strong forces of attraction)

• high density

• Good conductors of heat and electricity (delocalized electros)

• Malleable, soft (layers of atoms can slide over each other whilst maintaining the attraction forces)

Complete the table

Limitations of the simple model

• there are no forces between spheres and atoms, molecules and ions are solid spheres - this is not true

what does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?

• The strength of the forces between the particles of the substance.

• the nature of particles involved depends on the type of bonding and the structure of the substance.

• The stronger the forces between the particles, the higher the melting point and boiling point of the substance

A pure substance will melt or boil at? What about the mixture?

• A fixed temperature.

• A mixture will melt over a range of temperatures

three states of matter

• solid

• liquid

• gas

half equations for electrolysis of the aqueous solution of KCl

half equations for the electrolysis of the aqueous solution of H₂SO₄

properties of noble gas

• non-metals

• colorless gases

• low boiling points, it increases down the group, as atoms get heavier

• unreactive (full outer shell, they don’t easily accept or lose electrons)

law of conservation of mass

the law of conservation of mass states that no atoms are lost or made during a chemical reaction so that the mass of the products equals the mass of the reactants

relative atomic mas (RAM)

this is the average mass of an atoms in an element taking into account masses and abundance of its isotopes, relative to 1/12 of the masses of one carbon-12 atom

relative formula mass (RFM)

this is the sum of RAM’s of all atoms in the formula

Avogadro’s Constant

• this is the number of atoms, molecules or ions in a mole of a given substance

• the value of the constant is 6.02 × 10²³

formula that links mass, molecular mass and moles together

mass (g) = mr x moles

what is meant by a limiting reactant in a chemical reaction

• in a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used

• the reactant that is completely used up is called the limiting reactant because it limits the amount of products formed

the formula that links concentration, mole/mass and volume together

• concentration (g per dm³ ) = mass(g)/volume (dm³)

• concentration (mol per dm³ ) = # of moles/volume (dm³)

molar volume of a gas at room temperature and pressure

1 mole of a gas at room temperature and pressure occupies 24 dm³

titration

this is a technique for finding the concentration of a solution by reacting a known volume of this solution with a solution of known concentration

why is it not always possible to obtain the theoretical amount of product in a chemical reaction

• the reaction may not go to completion because it is reversible

• some of the product may be lost when it is separated from the reaction mixture

• some pf the reactants may react in ways different to the expected reaction (side reactions may occur)

how is a percentage yield of a product in a chemical reaction

what is an atom economy

• this is a measure of the amount of starting materials that end up as useful products

• it is a ratio of the relative formula mass of desired product/s to the sum of the relative formula masses of all reactants

electrolysis

• this is the passing of an electric current through ionic substances that are molten or in solution to break them down into elements

• ions are discharged (they lose/gain electrons) at electrodes to produce these

electrolyte

this is the liquid/ solution which conducts electricity

cathode and anode

• cathode is the negative electrode, reduction happens here

• anode is the positive electrode, oxidation happens here

how is aluminum manufactured

• this is done through electrolysis of aluminum oxide and cryolite

• large amounts of energy are needed to produce current

• cryolite is used because it lowers the melting point of aluminum oxide, reducing energy costs