Week 2 Necessary Vocabulary

Question 1

Element

Answer 1

A pure substance that cannot be broken down into simpler substances by ordinary chemical or physical techniques.

Question 2

Atom

Answer 2

The smallest unit that retains the chemical and physical properties of an element.

• Each atom has a few properties, most of which are based on the ability to attract electrons (its electronegativity) and hold energy in alternative stable states

Question 3

Atomic number (relate to number of protons and electrons)

Answer 3

The number of protons in the nucleus of an atom.

• number does not vary and thus specifically identifies the atom

Question 4

Orbital

Answer 4

The region of space where the electron “lives” most of the time.

Question 5

Electron shell

Answer 5

In chemistry and physics, may be thought of as an orbit followed by electrons around an atom’s nucleus. Also known as principal energy level.

• most stable shells position the electrons closest to the nucleus, and as electrons are added they occupy higher level shells.
• first shell (I) may be occupied by a maximum of two electrons. The second (II) and third (III) shells can hold a maximum of eight electrons each. fourth, 18 electrons.
• Because an unfilled electron shell is less stable than a filled one, atoms with an incomplete outer shell have a strong tendency to interact with other atoms in a way that causes them to either gain or lose enough electrons to achieve a filled valence shell.

Question 6

Valence shell

Answer 6

The chemical behaviour of an atom depends primarily on the number of electrons in its outermost shell. This is referred to as the valence shell, which holds valence electrons.

Question 7

Valence electron

Answer 7

An electron in the outermost energy level of an atom.

Question 8

Chemical bond

Answer 8

Link formed when atoms of reactive elements combine into molecules.

Question 9

Covalent bond

Answer 9

Bond formed by electron sharing between atoms.

• Biologically, a covalent bond acts more permanently and we find structures held together by covalent bonds to be the most durable. Hence, calling these entities “molecules” is a more functional definition.
• covalent bonding capacity of an atom is equal to the number of valence shell electrons necessary to fill the shell
• Without covalent bonding, macromolecules, organelles, and cells would not have their structure and life would be impossible.

Question 10

Ionic bond

Answer 10

Form between atoms that gain or lose valence electrons completely.

• EN difference greater than 1.7
• their weaker associations are better suited for only certain interactions, usually those involving temporary associations.
  –> essential functions such as aligning protein subunits and setting up gradients.
• are common among the forces that hold ions, atoms, and molecules together in living organisms because these bonds have three key features:

1. They exert an attractive force over greater distances than any other chemical bond.
2. Their attractive force extends in all directions.
3. They vary in strength depending on the presence of other charged substances.

Question 11

Hydrogen bond

Answer 11

Noncovalent bond formed by unequal electron sharing between hydrogen atoms and oxygen, nitrogen, or sulfur atoms.

• Particles that are held together but must occasionally dissociate (e.g., separation of two molecules of DNA in the double helix, or temporary binding of a hormone to a receptor) are often held together by hydrogen bonds
• When numerous, hydrogen bonds are collectively strong and lend stability to the three-dimensional structure of molecules such as proteins.
• The property of hydrogen bonds allows proteins to interact reversibly, as well as nucleic acids to assemble during synthesis and separate when appropriate.

Question 12

Molecule

Answer 12

A group of atoms held together with covalent bonds.

Question 13

hydrocarbon

Answer 13

Molecules consisting of carbon linked only to hydrogen atoms are called hydrocarbons

Question 14

Electronegativity

Answer 14

The measure of an atom’s attraction for the electrons it shares in a chemical bond with another atom

• The more electronegative an atom is, the more strongly it attracts shared electrons.

Question 15

Hydrophilic molecules

Answer 15

Refers to polar molecules that associate readily with water.

Question 16

Hydrophobic molecules

Answer 16

Refers to nonpolar substances that are excluded by water and other polar molecules.

Question 17

Geometric isomers

Answer 17

Atoms are in the same order (same number and types of atoms, and bonds), but have different spatial arrangements.

Question 18

Isomers (cis and trans)

Answer 18

• Two or more molecules with the same chemical formula but different molecular structures are called isomers.
• Cis isomers contain functional groups on the same side of the carbon chain. (double bond)
• Trans isomers contain functional groups that are located on the other sides of the double bond.
• Typically, one of the two forms enters much more readily into cellular reactions; just as your left hand does not fit readily into a right-hand glove, enzymes (proteins that accelerate chemical reactions in living organisms) fit only one of the two forms of an enantiomer.

Question 19

Polar Covalent Bond

Answer 19

Bond in which electrons are shared unequally.

• EN difference between 0.4-1.7
• the atom that attracts the electrons more strongly carries a partial negative charge (denoted by the symbol σ - )
• the atom deprived of electrons carries a partial positive charge (denoted by the symbol σ +
• atoms carrying partial charges give the molecule partially positive and negative ends; this is referred to as polarity, and the molecule is termed polar.

Question 20

Non-polar Covalent bond

Answer 20

a type of chemical bond that is formed when electrons are shared equally between two atoms.

• EN difference between 0-0.3