ATI TEAS Chemistry Summary

The atomic number is the number of protons in an atom. Every oxygen atom has 8 protons. (A neutral atom also has the same number of electrons, 8.)

Wrong choices

• 16: 16 is the usual mass number of oxygen (protons + neutrons).
• 4: This is half the atomic number.
• 2: This has no connection to the atomic number.

The pH scale runs from 0 to 14. Below 7 is acidic, 7 is neutral, and above 7 is basic. A pH of 3 is acidic.

Wrong choices

• pH 7: pH 7 is neutral, like pure water.
• pH 9: A pH above 7 is basic.
• pH 12: pH 12 is strongly basic.

Atoms have three main particles: protons (positive) and neutrons (no charge) in the nucleus, and electrons (negative) moving around the nucleus.

Wrong choices

• Proton: Protons have a positive charge.
• Neutron: Neutrons have no charge.
• Nucleus: The nucleus is the atom's center and has an overall positive charge from its protons.

A change from liquid to gas is vaporization. Boiling is vaporization throughout the liquid; evaporation is vaporization at the surface.

Wrong choices

• Condensation: Condensation is gas turning into liquid, the opposite change.
• Melting: Melting is solid turning into liquid.
• Sublimation: Sublimation is solid turning directly into gas.

A balanced equation has the same number of each kind of atom on both sides.

1. Left side of 2H₂ + O₂: H = 2 × 2 = 4, O = 2
2. Right side of 2H₂O: H = 2 × 2 = 4, O = 2 × 1 = 2

Both sides have 4 H and 2 O, so it is balanced.

Wrong choices

• H₂ + O₂ → 2H₂O: Hydrogen is not balanced: 2 atoms on the left, 4 on the right.
• H₂ + O₂ → H₂O: Oxygen is not balanced: 2 atoms on the left, 1 on the right.
• 2H₂ + 2O₂ → 2H₂O: Oxygen is not balanced: 4 atoms on the left, 2 on the right.

Sodium (a metal) easily loses one electron, and chlorine (a nonmetal) easily gains one. The electron transfers from Na to Cl, making Na⁺ and Cl⁻ ions. The attraction between these opposite charges is an ionic bond.

Wrong choices

• Sodium and chlorine share electrons equally (nonpolar covalent bond).: Equal sharing happens between similar atoms, such as two chlorine atoms, not between a metal and a nonmetal.
• Sodium and chlorine share electrons unequally (polar covalent bond).: NaCl forms by transfer of an electron, not sharing.
• A hydrogen atom links sodium and chlorine (hydrogen bond).: NaCl has no hydrogen, and hydrogen bonds are attractions between molecules.

Mass number = protons + neutrons.

1. Protons = atomic number = 17
2. Neutrons = 35 − 17 = 18

Check: 17 + 18 = 35.

Wrong choices

• 17: 17 is the number of protons.
• 35: 35 is the total of protons and neutrons.
• 52: This adds the two numbers instead of subtracting.

Elements in the same group (column) have the same number of valence electrons, the electrons in the outer shell. Because chemical reactions involve these outer electrons, elements in the same group behave similarly. Na and K each have one valence electron.

Wrong choices

• They have the same number of protons.: Each element has its own number of protons; Na has 11 and K has 19.
• They have the same atomic mass.: Their atomic masses are different.
• They are both noble gases.: Noble gases are in the far-right column and rarely react; Na and K are metals.

Concentration = amount of solute ÷ volume of solution.

1. 500 mL = 0.5 L
2. 20 g ÷ 0.5 L = 40 g/L

Check: 40 g/L × 0.5 L = 20 g.

Wrong choices

• 10 g/L: This treats 500 mL as 2 L instead of 0.5 L.
• 4 g/L: The decimal point is off by a factor of 10.
• 25 g/L: This divides 500 by 20, which flips the fraction.

A reaction that absorbs heat from its surroundings is endothermic ("endo" = in). The surroundings, including your hand, lose heat, so the pack feels cold. A reaction that releases heat is exothermic ("exo" = out).

Wrong choices

• Exothermic: An exothermic reaction gives off heat and feels warm.
• Combustion: Combustion is burning, which releases heat and light.
• Neutralization: Neutralization is an acid reacting with a base; it does not describe heat being absorbed.