SCI131 MIDTERM EXAMINATIONS

Element

A pure substance that cannot be separated into simpler substances by physical or chemical means.

Atom

The smallest piece of matter that still retains the property of the element.

Nucleus

Protons and neutrons are found in a small, positively-charged center of the atom; surrounded by a cloud containing electrons.

Scaled-down models,

Allow you to see something too large to see all at once or something that has not been built yet

Scaled-up models

Often used to visualize things that are too small to see.

Atomos

The ancient Greek philosophers Leucippus and Democritus proposed that elements consist of tiny, solid particles that cannot be subdivided.

Solid Sphere Model

Each element has unique atoms. Atoms of a particular element are identical, but different in another element.

John Dalton

Proposed the solid sphere model and the father of atomic theory.

Law of conservation of mass

There is no detectable change in mass during an ordinary chemical reaction.

Law of constant composition

A chemical compound always contains the same elements in the same proportion by mass.

Law of multiple proportions

• If two elements can be combined to form several possible compounds, then

• The ratios of the masses of the second element, which combine with a fixed mass of the first element, will be ratios of small whole numbers.

Revisions to Dalton’s Atomic Theory

• Atoms are not indestructible, as they still consist of smaller particles

• Atoms in one element may differ in mass. They are identical only in some basic respects

Plum Pudding Model

Atoms were composed primarily of a very massive, positively charged blob. Embedded in this blob were negatively-charged electrons.

Joseph John Thompson

Proponent of Plum Pudding Model, discovered electrons

Nuclear Model

An atom is made up of a very dense, positively charged nucleus surrounded primarily by empty space in which electrons could be found.

Ernest Rutherford

Proponent of Nuclear Model; discovered protons

Gold foil experiment

Proved that an atom consists of nucleus and electrons for the Plum Pudding Model

Bohr’s Model

The electron to be rotating in orbits around the nucleus and that an electron had to be in one specific orbit of another (planetary model)

Neils Bohr

Proponent of Bohr’s model

Quantum Mechanics Model

Different electrons have different amounts of energy and thus occupy different regions within the atom. Furthermore, the energies of electrons are quantized, or restricted to having only certain values.

Erwin Schrödinger

Proponent of Quantum Mechanics Model

Electron

Negative charged particle

Proton

Positively charged particle

Neutron

Subatomic particle that bears no electric charge

James Chadwick

Discovered the neutron

Atomic number

Describes the number of protons in an atom, denoted as Z

Atomic mass or mass number

Describes the number of protons and neutrons in an atom, denoted as A

Nuclear Reaction

A reaction that involves a change in an atom’s nucleus, which may lead to the formation of a new element

Radioactive decay

Unstable nuclei lose energy by emitting radiation in a spontaneous process

Alpha Radiation

Consists of a stream of helium-4 nuclei known as alpha particles, denoted as 4|2 He or a

Beta Radiation

Consists of streams of beta particles, which are high-speed electrons emiited by an unstable nucleus

Gamma Radiation

Consists of high-energy photons. Neither changes

Positron Emission

Emits a positron.

Electron Capture

Capture by the nucleus of an electron from the electron cloud surrounding the nucleus

Hydrogen Fusion

Fundamental nuclaer reaction in stars

Main sequence star

Any star that is fusing hydrogen in its core

Proton-proton chain

From two protons to helium-4 which releases two hydrogen atoms from the protons before

Carbon-Nitrogen-Oxygen-Cycle

A nuclear reaction by which stars produce helium from a hydrogen using carbon, nitrogen, and oxygen as catalysts.

Triple Alpha Process

• Once all hydrogen has been converted into helium, carbon forms via the ________

1. Two helium-4 nuclei come together and form beryllium-8

2. Beryllium-8 is further attacked by a helium-4 and forms a stable carbon-12

Nuclear Transmutations

• A nucleus can change identity if it is struck by a neutron or by another nucleus

• Process of changing one element into anotherby altering the number of protons in its nucleus

Transuranium Elements

Used to produce the elements with atomic number above 92

Chemical bonding

Attractive force holding atoms or ions together to make a more stable state for the whole system compared to individual atoms

Stability

Results to a more stable state, atoms bond because they want _____

Electronegativity

Measure of the tendency of an atom to attract a bonding pair of electrons, which chemical bonding is dependent here.

Octet Rule

Atoms are stable if they have 8 valence electrons

Ionic Bonding

Transfer of electrons from the metal to the nonmetal, due to electrostatic attractions between oppositely charged ions

Cation

Atom that loses one or more electrons to become a positively charged ion

Anions

Molecules are formed by the sharing of electrons between nonmetals.

Covalent Bond

Molecules are formed by the sharing the electrons between nonmetals, atom involved in covalent bonding arrange themselves to achieve the greatest energetic stability.

Nonpolar covalent bond

Valence electrons are shared equally

Polar covalent bond

Valance electron are shared unequally

Bond polarity

Measure of how equally the electrons in a bond are shared between the two atoms of bonds.

Dipole moment

a measure of the amount of charge separation in the molecule

Bond dipole

Refers to the dipole moment due only to the two atoms in that bond.

Intermolecular Forces

Forces that exist between separate molecules that influence the physical properties of substances

London Dispersion Forces

• Attracted between an instantaneous dipole and induced dipole (nonpolar)

• Weakest IMF because it is sudden

• More electron = strong LD force (polarizability)

Dipole-dipole Forces

• Electrostatic attractions between the partially positive end of one molecule and the partially negative end of another molecule.

• Presence of a permenant dipole moment in polar molecules, as it exists in all polar molecules

Hydrogen bond

• Special kind of dipole-dipole and the strongest

• H (hydrogen) atom attracts to a non-binding electron of a nearby atom / molecule

• Usually F, O, N

Ion-Dipole Forces

• Ion (changed atom) bonded to a polar molecule

• Cations attracted to negative end of the dipole

• Anion attracted to positive end of the dipole

• Always metal or ionic elements

Collision Theory

Atoms must collide with enough energy to react to:

• Form new product

• React & Produce molecule

Reaction Rate

The more often reactant molecules colide, the more often they react with one another, and the faster the _____

(1) collide

(2) sufficient energy

(3) with the proper orientation

Steps for Collision Theory

Activated complex

Temporary, unstable arrangement of atoms where old bonds are breaking and new bonds are forming (also called transition state)

Activation energy

Minimum amount of energy that reacting particles must have to form the activated complex and lead to a recation

Exothermic reactions

May occur spontaneously and result in higher randomness or entropy. Produces heat or may even be explosive (heat is released)

Endothermic reactions

Cannot occur spontaneously, as work must be done in order to get these reactions to occur (heat is absorbed)

Nature of Reactant

The more readily the reactants collude, the more rapidly they react.

• Homogenous reactions are often fast, while heterogenous that have solids are fast if surface area is increased

Concentration

Increasing the reactant concentration generally increases the reaction rate since there are more molecules that can have more collisions.

Temperature

Increasing temperature increases reaction rate due to kinetic energy; molecules more quietly.

Catalysts

• Speed up reactions w/o being overall balanced equation

• Affects kind of collision, changes mechanism and lowering action energy.

Energy Sources

Refers to means by which we generate power to meet our needs

Fossils Fuels

• Formed from ancient plants & animals

• Converts organic matter into carbon-rich substance and when burned, generates energy (can also produce pollution)

• often caled dirty energy sources because using them comes at a high—and often irreversible cost to the environment.

Petroleum

• crude oil refined into gasoline, diesel, etc.

• naturally occurring flammable liquid

• made up of carbon; extracted through driling, hydraulic fracture or fracturing

Coal

• rock found near the Earth’s surface and most abundant

• made up of carbon from living organisms

• extracted through surface mining and undergrund mining

• combustibe block sediments

Natural Gas

• Mixture of gases trapped under the Earth’s rock ayers

• Mass amounts of methane (CH₄)

Carbon emissions

The amount of carbon dioxide these fuels release into the atmosphere add up over generations and cannot be taken back.

Alternative Energy

Broadly refers to any energy that is not extracted from a fossil fuel, but not necessarily only from a renewable source.

Renewable energy

Includes sources such as sun and wind that occur naturally and continuously

Wind power

Created when wind spins a turbine, or a windmill, which can be located on land or offshore

Solar power

Harnesses the sun’s energy in two ways

• converting the sun’s light directly into electricity (when sun is out)

• solar thermal energy to create electricity (even when sun is down)

Hydropower

Created when rapidly flowing water turns turbines inside a dam, generating electricity

Geothermal Energy

Heat energy from the Earth; reservoirsof hot water that exist or are human-made at varying temperatures & depths below Earth’s surface

Nuclear Energy

Produced at power plants by the process of nuclear fission. The enegry created during nuclear reactions is harnessed to produced electricity

Biofuels

Produced by organic materials that contains stored energy

• Burn wood for fire / liquid biofuel

Disinfectant

A chemical that destroys all disease-causing organisms (pathogens).

• Destroys 99.999% of pathogens within 5 to 10 minutes

Sanitizer

A product that reduces germs on surfaces to levels considered safe by public health codes or regulations.

• Destroy 99.999% of pathogens within 30 seconds

Abrasives

Rough or gritty, they clean surfaces by creating friction that lifts off spots and stains from a surface.

Physical abrasives

Includes sandpaper, plastic, and nylon meshes, scrubbing pads, and steel wool

Mineral abrasives

Composed of particles like baking soda, powdered borax, and salt, which are considered natural cleaners

Chemical abrasives

Often referred to as scouring powders and are used to kill bacteria in addition to general surface cleaning.

dichloros-triazinetrione

Common chemicals used in commercial products that contain bleach

Acid

Used to remove mineral deposits, rust stains, and hard water deposits. They can remove discoloration from some metals and effective in both cleaning and disinfecting surfaces.

Acetic acid

Acid in clear white vineger and is a natural all-purpose cleaning agent. It is best for general household cleaning on surfaces that can tolerate a strong, acidic product.

Citric acid

a natural substance found in lemons, limes, oranges, and grapefruits. It is nontoxic, antibacterial, and antiseptic. Some commercial products that contain citric acid are waterbased and may cause corrosion or rust on metals.

Cream of tartar

a very mild acid salt. Made into a paste with water, it can be used to clean brass and copper, brighten aluminum, remove rust, and freshen coffee makers.

Phosphoric acid

a clear, colorless, odorless liquid. It is very mild, yet more acidic than vinegar or lemon juice. Commonly used for rust removal, it works quite well on most types of bathroom stains.

Hydrochloric acid

a mixture of common table salt and sulfuric acid. Concentrated solutions of hydrochloric acid are extremely corrosive.

• Diluted solutions are commonly found in household cleaning products.

• Very dilute solutions are only mildly corrosive.

Hydrofluoric acid

a commercial rust remover that will burn the skin. Keep this one away from glass windows or glass products.

Oxalic acid

a bleaching agent that is an effective rust remover. It is poisonous and corrosive.

Sodium bisulfate

can be found in toilet bowl cleaners. It is a compound made by combining sodium, hydrogen, sulfur, and oxygen ions. It is a poison and should be used with extreme caution.