Atoms, Chemical Bonds, Water, and pH

Comprehensive practice flashcards covering atomic structure, chemical bonds, isotopes, electronegativity, properties of water, pH, and buffers based on lecture slides.

What three subatomic particles make up an atom, and where are they located?

Protons (positively charged) and neutrons (neutral) are found in the nucleus, while electrons (negatively charged) are found in orbitals surrounding the nucleus.

How is the atomic number of an element defined?

The atomic number tells the number of protons in an atom (which also equals the number of electrons in an electrically neutral atom). Every atom of a particular element has the same number of protons.

How is atomic mass determined?

Atomic mass is determined by the number of protons and neutrons an atom has, with each proton and neutron having a mass of approximately $1\,amu$. Electrons have so little mass that they are not included in the mass calculation.

How does modern physics define an electron orbital, and what is its capacity limit?

An orbital is an area around a nucleus where an electron is most likely to be found. No orbital can contain more than two electrons.

How does an electron's potential energy relate to its position relative to the nucleus?

Electrons have potential energy related to their position; electrons located farther from the nucleus have more energy.

What is the octet rule?

The octet rule states that atoms tend to establish completely full outer energy levels, typically requiring eight valence electrons (or two for the innermost level).

What chemical process is depicted in this diagram showing an electron transfer between two atoms?

Oxidation (the loss of an electron) and reduction (the gain of an electron).

What are isotopes, and what is meant by radioactive half-life?

Isotopes are atoms of a single element that possess different numbers of neutrons. Radioactive isotopes are unstable, and their half-life is the time it takes for one-half of the atoms in a sample to decay.

Which four elements make up $96.3\%$ of human body weight?

Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur (CHNOPS)

What is the difference between ionic and covalent chemical bonds?

In ionic bonds, atoms transfer electrons to form charged ions that attract each other tightly. In covalent bonds, atoms share two or more valence electrons.

How is an ionic bond formed between sodium ($\text{Na}$) and chlorine ($\text{Cl}$), as shown in this figure?

The sodium atom loses an electron to become a positively charged cation ($\text{Na}^+$), and the chlorine atom gains an electron to become a negatively charged anion ($\text{Cl}^-$). Their opposite charges attract to form an $\text{NaCl}$ crystal.

How do electronegativity differences determine whether a covalent bond is polar or nonpolar?

Electronegativity measures an atom's ability to attract electrons. An electronegativity difference of $0.0 - 0.4$ forms a nonpolar covalent bond (equal sharing), whereas a difference of $0.5 - 1.9$ forms a polar covalent bond (unequal sharing).

Why is the bond in methane ($\text{CH}_4$) considered nonpolar given carbon's electronegativity of $2.6$ and hydrogen's of $2.2$?

Because the difference in electronegativity is $2.6 - 2.2 = 0.4$, which falls within the $0.0 - 0.4$ range for nonpolar covalent bonds.

What is a hydrogen bond?

A hydrogen bond is a weak attraction between a highly electronegative atom (such as $\text{N}$, $\text{O}$, or $\text{F}$) and a hydrogen atom participating in a separate polar covalent bond.

How do cohesion and adhesion differ in water molecules?

Cohesion occurs when water molecules stick to other water molecules by hydrogen bonding. Adhesion occurs when water molecules stick to other polar molecules by hydrogen bonding.

What property of water allows insects like the water strider pictured here to walk on water?

Cohesion between water molecules, which creates surface tension.

What property causes water to rise higher in narrower glass tubes, as demonstrated in this setup?

Adhesion between the polar water molecules and the polar glass surface, driving capillary action.

What are three key thermal and physical properties of water resulting from hydrogen bonding?

1. High specific heat (requires large energy input to change temperature).

2. High heat of vaporization (evaporation cools surfaces).

3. Solid water is less dense than liquid water (ice floats, causing bodies of water to freeze top-down).

What structure forms around dissolved salt ions when water acts as a solvent, as shown in this diagram?

Hydration shells, where partially negative oxygen atoms surround $\text{Na}^+$ ions and partially positive hydrogen atoms surround $\text{Cl}^-$ ions.

How are acids and bases defined with respect to hydrogen ion concentration $[H^+]$?

An acid is any substance that dissociates in water to increase $[H^+]$ and lower pH.

A base is any substance that combines with $[H^+]$ in water to decrease $[H^+]$ and increase pH.

How do pH buffers resist changes in the pH of a solution?

Buffers resist pH changes by releasing hydrogen ions ($H^+$) when a base is added, and absorbing hydrogen ions ($H^+$) when an acid is added, keeping $[H^+]$ constant.

What reversible chemical reaction represents the biological buffer system involving carbon dioxide and water?

$$\text{H}_2\text{O} + \text{CO}_2 \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+$$

(Water + Carbon dioxide $\rightleftharpoons$ Carbonic acid $\rightleftharpoons$ Bicarbonate ion + Hydrogen ion).