chapter two - atomic structure

According to the chemical context of life, organisms and their environments are subject to the basic laws of _____ and _____.

physics; chemistry

Term: Element

Definition: A substance that cannot be broken down to other substances by chemical reactions.

What percentage of the 92 natural elements are considered essential elements required for life?

About $20-25\%$.

Which four elements make up approximately $96\%$ of living matter?

Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), and Nitrogen ($N$).

What is the most abundant element in the human body by percentage of body mass?

Oxygen ($O$), at $65.0\%$.

In the human body, Carbon ($C$) accounts for approximately _____ of total body mass.

$$18.5\%$$

What is the definition of a trace element?

An element required by an organism in minute quantities, making up less than $0.01\%$ of mass.

Term: Atom

Definition: The smallest unit of matter that still retains the properties of an element.

What is the electrical charge associated with a proton?

Positive charge.

What is the electrical charge associated with an electron?

Negative charge.

Which subatomic particle carries no electrical charge?

The neutron.

Where are neutrons and protons located within an atom?

In the atomic nucleus.

Electrons form a "cloud" of _____ charge around the atomic nucleus.

negative

What specifically determines the atomic number of an element?

The number of protons in its nucleus.

Term: Mass Number

Definition: The sum of protons plus neutrons in the nucleus of an atom.

Which value can be used to approximate an atom's total atomic mass?

The mass number.

An electron's state of potential energy is referred to as its _____ or electron shell.

energy level

How does an electron move to a shell further away from the nucleus?

By absorbing energy.

When an electron loses energy, it moves to an electron shell that is _____ the nucleus.

closer to

What is the maximum number of electrons the first electron shell can accommodate?

Two electrons.

The second electron shell can accommodate a maximum of _____ electrons.

eight

The chemical behavior of an atom is primarily determined by the distribution of electrons in its _____.

electron shells

Term: Valence Electrons

Definition: The electrons located in the outermost electron shell of an atom.

What is the term for the outermost electron shell of an atom?

The valence shell.

Why are elements like Helium, Neon, and Argon chemically inert?

They have a full valence shell.

Term: Orbital

Definition: The three-dimensional space where an electron is found $90\%$ of the time.

What is the maximum number of electrons that any single orbital can accommodate?

Two electrons.

The second electron shell consists of one "s" orbital and _____ "p" orbitals.

three

What is the minimum number of orbitals required to accommodate the ten electrons of Neon?

Five orbitals.

Atoms with incomplete valence shells interact to stay close together through attractions called _____.

chemical bonds

Term: Covalent Bond

Definition: The sharing of a pair of valence electrons by two atoms.

In a covalent bond, the shared electrons count as part of _____ atom's valence shell.

each

Two or more atoms held together by covalent bonds constitute a(n) _____.

molecule

What is the difference between a single covalent bond and a double covalent bond?

A single bond shares one pair of electrons, while a double bond shares two pairs.

Term: Valence

Definition: The bonding capacity of an atom, usually equaling the number of electrons required to complete its outermost shell.

What constitutes a chemical compound?

A combination of two or more different elements.

Term: Electronegativity

Definition: An atom's particular attraction for the electrons in a covalent bond.

How does high electronegativity affect the shared electrons in a covalent bond?

The atom pulls the shared electrons more strongly toward itself.

In a(n) _____ covalent bond, the atoms share the electrons equally.

nonpolar

What is a primary advantage of the reversibility of weak chemical bonds in biological molecules?

It allows molecules to be held in functional forms that can be easily rearranged.

Term: Hydrogen Bond

Definition: An attraction formed when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.

What state is reached when the forward and reverse reaction rates are equal?

Chemical equilibrium.

At chemical equilibrium, the relative _____ of reactants and products do not change.

concentrations

Which subatomic particle is directly involved in the chemical bonding between atoms?

The valence electron.

Trace elements like Iron ($Fe$) and Iodine ($I$) make up less than _____ of body mass.

$$0.01\%$$

List the four kinds of chemical bonds relevant to life mentioned in the source material.

Covalent bonds, Ionic bonds, Hydrogen bonds, and Van der Waals interactions.

What is the structural formula abbreviation for a double bond between two Oxygen atoms?

$$O=O$$

In a water molecule ($H_2O$), how many single covalent bonds are present?

Two.

Why are many pharmaceuticals manufactured as salts in powder form?

They are very stable for storage but can be easily dissolved in water before use.

A structural formula like $H-H$ uses a line to represent a(n) _____.

single bond (or shared pair of electrons)