BISC 221 - Lecture 2 (Biochemistry) - Midterm 1

How many of the 92 elements are essential to life?

About 25 of the 92 elements are essential to life

Which elements make up 96% of living matter?

Carbon, hydrogen, oxygen, and nitrogen

What percentage of living matter is made up by carbon, hydrogen, oxygen, and nitrogen?

96%

What elements make up most of the remaining 4% of living matter?

calcium, phosphorus, potassium, and sulfur

What are trace elements?

those required by an organism in minute quantities

What does each element consist of?

unique atoms

What is an atom?

the smallest unit of matter that still retains the properties of an element

What are atoms composed of?

subatomic particles

What relevant subatomic particles are included?

Neutrons Protons Electrons

What electrical charge do neutrons have?

no electrical charge

What electrical charge do protons have?

positive charge

What electrical charge do electrons have?

negative charge

What forms the atomic nucleus?

Neutrons and protons

What forms a cloud around the nucleus?

Electrons

How do neutron mass and proton mass compare?

almost identical

In what units are neutron mass and proton mass measured?

daltons

Why are electrons ignored when calculating the total mass of an atom?

Electrons are so small

What is energy?

the capacity to cause change

What is potential energy?

the energy that matter has because of its location or structure

How do the electrons of an atom differ?

in their amounts of potential energy

What is an electron’s state of potential energy called?

its energy level, or electron shell

What are valence electrons?

those in the outermost shell, or valence shell

What mostly determines the chemical behavior of an atom?

the valence electrons

What are elements with a full valence shell?

chemically inert

What is an orbital?

the three-dimensional space where an electron is found 90% of the time

What does each electron shell consist of?

a specific number of orbitals

What can atoms with incomplete valence shells do?

share or transfer valence electrons with certain other atoms

What do these interactions usually result in?

atoms staying close together

What holds atoms close together in these interactions?

attractions called chemical bonds

What is a covalent bond?

the sharing of a pair of valence electrons by two atoms

In a covalent bond, how are shared electrons counted?

as part of each atom’s valence shell

What is a molecule?

two or more atoms held together by covalent bonds

What is a single covalent bond?

the sharing of one pair of valence electrons

What is a double covalent bond?

the sharing of two pairs of valence electrons

What is bonding capacity called?

the atom’s valence

Between what atoms can covalent bonds form?

atoms of the same element or atoms of different elements

What is a compound?

a combination of two or more different elements

What is electronegativity?

an atom’s attraction for the electrons in a covalent bond

What happens the more electronegative an atom is?

the more strongly it pulls shared electrons toward itself

What is the electronegativity of oxygen?

3.5

What is the electronegativity of nitrogen?

3.0

What is the electronegativity of sulfur?

2.5

What is the electronegativity of carbon?

2.5

What is the electronegativity of phosphorus?

2.1

What is the electronegativity of hydrogen?

2.1

What happens in a nonpolar covalent bond?

the atoms share the electron equally

What happens in a polar covalent bond?

one atom is more electronegative, and the atoms do not share the electron equally

What does unequal sharing of electrons cause?

a partial positive or negative charge for each atom or molecule

What is a hydrogen bond?

forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom

In living cells, what are usually the electronegative partners in hydrogen bonds?

oxygen or nitrogen atoms

What is surface tension?

a measure of how hard it is to break the surface of a liquid

Why does water have an unusually high surface tension?

hydrogen bonding between the molecules at the air-water interface and to the water below

What sometimes happens during bonding between atoms?

Atoms sometimes strip electrons from their bonding partners

What is an example of electron transfer?

the transfer of an electron from sodium to chlorine

What happens to atoms after the transfer of an electron?

both atoms have charges

What is a charged atom or molecule called?

an ion

What is a cation?

a positively charged ion

What is an anion?

a negatively charged ion

What is an ionic bond?

an attraction between an anion and a cation

What are compounds formed by ionic bonds called?

ionic compounds, or salts

Where are salts often found in nature?

as crystals

What is an example of a salt?

sodium chloride (table salt)