TEAS Chemistry

What are the three subatomic particles that compose an atom, and what are their respective charges and relative masses?

• Proton: Charge of +1, mass of 1 amu

• Neutron: Charge of 0 (neutral), mass of 1 amu

• Electron: Charge of -1, mass of ~0 amu (negligible mass)

What defines an element's atomic number?

The total number of protons in the nucleus of an atom.

How is the atomic mass of an atom calculated?

By adding the number of protons and neutrons found in the nucleus.

What are isotopes?

Atoms of the same element that have the same number of protons but different numbers of neutrons.

What is an ion, and how does a sodium (Na) atom become a positively charged ion (Na+)?

• An ion is a positively or negatively charged atom or molecule.

• Sodium becomes Na+ by losing an electron, leaving it with more protons than electrons.

How are elements arranged in the periodic table?

From left to right by increasing atomic number (number of protons).

What do groups (vertical columns) on the periodic table indicate?

Elements with similar properties, reflecting the same number of valence (bonding) electrons in their outermost shell.

What do periods (horizontal rows) on the periodic table indicate?

The energy level/shell of the valence electrons (represented by electron "highways" containing specific orbital lanes).

What are the four types of subshell orbitals and the maximum number of electrons each can hold?

• s orbital: max 2 electrons

• p orbital: max 6 electrons

• d orbital: max 10 electrons

• f orbital: max 14 electrons

Why do atoms form chemical bonds, and which groups of elements do not naturally react?

• Atoms react to achieve stability by filling their valence shell.

• Noble gases (like helium and neon) have full valence shells, are completely stable, and do not react (referred to as inert gases).

What is the difference between intensive and extensive physical properties?

• Intensive properties do not depend on the amount of substance present (e.g., density, boiling point).

• Extensive properties change depending on the amount of matter present (e.g., mass, volume).

How is density defined, and why is it useful?

• Density is the ratio of mass to volume.

• It relies on a substance's unique structure rather than sample size, making it useful for identifying unknown substances.

What does the Kinetic Molecular Theory state about molecules?

• All matter is made of molecules in constant motion above absolute zero (0 K or -273°C).

• Heat overcomes intermolecular forces, causing molecules to move further apart without breaking bonds within a single molecule.

How do molecular motion and arrangement differ in solids, liquids, and gases?

• Solids: Packed tightly in an orderly pattern with only vibrational motion (definite shape and volume).

• Liquids: Less ordered and further apart, exhibiting vibrational and translational motion (definite volume, no definite shape).

• Gases: Rapidly moving and spread far apart with no definite shape or volume, and are highly compressible.

What two conditions determine the phase of a substance?

Temperature (increasing moves particles apart) and pressure (increasing packs particles closer together).

What is sublimation and what is an example?

• Sublimation is the transition where a solid converts directly into a gas without passing through the liquid state.

• An example is solid carbon dioxide (dry ice) changing directly to gas at room temperature.

What is deposition?

Deposition is the opposite of sublimation, where a gas converts directly into a solid (such as water vapor forming frost on windows in cold temperatures).

What is a valence electron?

An electron in an outer orbital that can form bonds with other atoms.

How do metals typically behave in chemical reactions based on their ionization energy and electronegativity?

Metals have low ionization energies and low electronegativities, meaning they tend to lose electrons and become positively charged cations.

How do nonmetals typically behave in chemical reactions?

Nonmetals on the right side of the periodic table have high electronegativities, meaning they tend to gain electrons to become negatively charged anions.

What characterizes an ionic bond?

It forms when there is a large difference in electronegativity (such as between metals and nonmetals), resulting in the complete transfer of electrons from the metal to the nonmetal.

What characterizes a covalent bond?

It occurs between two nonmetals where electrons are shared rather than transferred because there is not a sufficient difference in electronegativity.

Why is water considered a polar covalent molecule?

Because of the strong electronegativity of oxygen pulling at the shared electrons, making the oxygen side partially negative and the hydrogen side partially positive.

What are the components of a chemical equation?

Reactants are on the left side of the equation (starting materials), a reaction sign (→) shows the direction, and products are on the right side (substances formed).

Why must chemical equations be balanced?

Because the total mass of the elements entering and exiting the reaction does not change, meaning there must be the exact same number of atoms for each element on both sides.

What do the numbers placed in front of chemical formulas (coefficients) represent in a balanced equation?

They adjust the quantities to balance the atoms, and in terms of equations, coefficients represent moles.

What is a mole and what is Avogadro's number?

• A mole is a unit of a substance used to measure mass equal to its atomic or molecular mass in grams.

• Avogadro's number is 6.022×1023, which is the exact number of particles in one mole of anything.

What factors can alter the rate of a chemical reaction?

Pressure, concentrations of reactants and products, temperature, and the presence of catalysts.

How does temperature affect endothermic versus exothermic reactions?

• An increase in temperature increases the rate of an endothermic reaction (where heat is required).

• An increase in temperature slows down an exothermic reaction (where heat is released).

How do pressure and reactant concentration affect reaction rate?

• Increasing pressure on a gas-phase reaction increases the chance of molecular collisions, speeding up the rate.

• Increasing reactant concentration increases the probability that reactants will collide and react.

What is chemical equilibrium?

A stage in a reversible chemical reaction where both reactants and products are present, and their concentrations no longer change because the forward and reverse reaction rates are equal.

What does Le Chatelier's principle state?

When a chemical reaction at equilibrium is perturbed, it responds by proceeding in a direction that restores equilibrium.

How do catalysts speed up chemical reactions?

They lower the activation energy (the minimum energy needed to initiate the reaction) without undergoing permanent chemical change themselves.

What makes water a polar molecule, and what properties does this polarity enable?

• Water has a negatively charged oxygen end and positively charged hydrogen ends.

• Its polarity allows it to form hydrogen bonds and exhibit strong cohesive and adhesive properties.

What is the difference between cohesion and adhesion in water?

• Cohesion is the tendency of similar molecules to stick together, which creates surface tension and allows water to travel through small capillaries without energy.

• Adhesion is the measure of how well dissimilar particles or surfaces cling to one another due to water's polarity.

Why does ice float in liquid water?

• Ice floats because it has a lower density than liquid water.

• Unlike water, most substances have greater densities in their solid form.

How do temperature changes affect the solubility of solid/liquid solutes versus gases?

• The solubility of most solid and liquid solutes increases with increasing temperature.

• The solubility of a gas decreases with increasing temperature.

What distinguishes saturated, unsaturated, and supersaturated solutions?

• A saturated solution holds the maximum possible amount of solute.

• An unsaturated solution has less than the maximum amount of solute dissolved.

• A supersaturated solution is created at higher temperatures, enabling more solute to dissolve than would normally be possible at lower temperatures.

Which concentration unit is temperature-dependent?

Molarity (mol/L) is temperature-dependent, whereas other units like molality, mass percentage, ppm, and ppb are independent of temperature.

What is diffusion?

Diffusion is the movement of any substance from areas of high concentration to areas of low concentration.

What is osmosis, and does it require energy?

• Osmosis is a specific type of diffusion where water moves passively across a semipermeable membrane from an area of high solvent concentration (low solute) to low solvent concentration (high solute) through aquaporins.

• It is a form of passive transport and does not require energy other than the kinetic energy of moving molecules.

What is active transport?

Active transport is the movement of substances from areas of low to high concentration against a concentration gradient, which requires the use of energy.

What does an acid produce in an aqueous solution, and how does it act regarding protons?

• An acid produces hydrogen ions (H+) in aqueous solution.

• It acts as a proton or hydrogen ion donor.

Why is hydrochloric acid (HCl) a strong acid, while acetic acid is a weak acid?

• HCl is a strong acid because it fully dissociates in water.

• Acetic acid is a weak acid because it does not fully dissociate or donate all of its hydrogen ions.

What does a base produce in an aqueous solution, and how does it act regarding protons?

• A base produces hydroxide ions (OH−) in aqueous solution.

• It acts as a proton acceptor.

What is the pH scale, and how are acidic, neutral, and basic solutions categorized on it?

• pH is a logarithmic scale (pH=−log[H+]) used to express acidity or basicity.

• A pH<7 is acidic, pH=7 is neutral, and pH>7 is basic.

What is a buffer and what is its primary function?

• A buffer is a solution of a weak acid and its conjugate base (or weak base and its conjugate acid).

• It helps resist changes in pH by absorbing excess H+ or OH− ions.

Which buffer system maintains the pH of human blood?

The carbonic acid (H2​CO3​) and bicarbonate (HCO3−​) buffer system.

What are the products of an acid-base neutralization reaction?

• Water, formed when H+ from the acid combines with OH− from the base.

• A salt or ionic compound, resulting in a neutral system with a pH of 7 when equal moles of acid and base are used.