2. Chemical Context of Life

Question 1

What is an Element?

Answer 1

An Element is a substance that cannot be broken down to other substances by chemical reactions.

Question 2

What 4 elements make up 96.3% of our body mass

Answer 2

Oxygen

Carbon

Hydrogen

Nitrogen

Question 3

How many elements are there in the human body

Answer 3

25

Question 4

What is a compound?

Answer 4

a compound is a substance consisting of two or more different elements combined in a fixed ratio

Examples:

NaCl → Sodium Chloride → 1:1 ratio

H₂0 → Water → 2:1 ratio

Question 5

What is an Atom

What is an atom composed of?

Answer 5

The smallest unit of matter that still retains the element’s properties

Atoms are composed of subatomic particles:

• A proton is positively charged.
• A neutron is electrically neutral.
• An electron is negatively charged.

Question 6

Atomic Number =

Atomic Mass =

What is the relation between protons and electrons?

Answer 6

• The atomic number of an element = the number of protons it has
• The Atomic Mass of an element = the number of protons + the number of neutrons it has
• there are an equal amount of electrons as there are protons (# of protons = # of electrons)
• The number of protons, the atomic number, determines which element it is.
• The unit for atomic mass is Dalton (Da).

Question 7

Elements are arranged on the periodic table according to the number of _________?

Answer 7

Protons

and since # electrons = # of protons it could also be said that it is arranged by number of electrons

Question 8

What are Isotopes?

Answer 8

Isotopes are different atomic forms of the same element.

Isotopes of the same element have the same number of protons but have a different number of neutrons

Question 9

What is a Radioisotope

Answer 9

An Unstable isotope which decays.

When the radioactive decay leads to a change in the number of protons, it transforms the atom to an atom of a different element

important as radioactive tracers in biological experiments, and for radiometric dating

Question 10

What is a Half-life?

Answer 10

A “parent” isotope decays into its “daughter” isotope at a fixed rate, expressed as the half life of the isotope –

The time it takes for 50% of the originally existing radioactive isotope to decay.

Question 11

Example

Answer 11

Question 12

Question 13

The chemical behavior of an atom depends mostly on?

An atom with a completed valence shell is _____?

Answer 13

The chemical behavior of an atom depends mostly on the number of electrons in its outermost shell

an atom with a completed valence shell is unreactive; that is it will not interact readily with other atoms.

Question 14

Electron Shells

How many electrons does the first shell hold?

” “ 2nd Shell holds?

” “ 3rd shell holds?

Answer 14

Electrons can exist only at certain energy levels : the electron shells. Electron fills from the 1st electron shell (the lowest energy level).

1st shell holds a max of 2 electrons

2nd shell holds a max of 8 electrons

3rd shell holds a max of 8 electrons

Question 15

Electron Orbitals

Answer 15

the 3 dimensional space where an electron is found 90% of the time.

Each single orbital holds a maximum of 2 electrons.

1st Shell:The first electron shell has only one spherical s orbital (called 1 s)

2nd Shell: the second shell has four orbitals: one large spherical s orbital (called 2 s) and three dumbbell shaped p orbitals (called 2 p orbitals)

3rd Shell: also have s and p orbitals as well as orbitals of more complex shapes.

Question 16

Electron shells vs Electron orbitals

Question 17

What is a valence shell?

What is a valence electron?

Answer 17

A valence shell is the outermost shell involved in bonding

Valence electrons are the outer electrons involved in bonding

Question 18

The reactivity of an atom arises from the presence of:

Answer 18

The reactivity of an atom arises from the presence of unpaired electrons in one or more orbitals of the atom’s valence shell.

Question 19

Exercise: For the three elements provide:

Atomic Number

Atomic Mass

Proton Number

Neutron Number

Electron Number

Electron Shell

Valence Shell

Valence Electron

Question 20

Why are electron shells and orbitals important?

Answer 20

1. Covalent bond
2. Ionic bond
3. Hydrogen bond
4. Van der Waals Interaction

Question 21

What is a Covalent Bond?

Answer 21

a covalent bond is the sharing of a pair of valence electrons by two atoms

Question 22

Answer 22

Question 23

What are Molecules/compounds?

What are the “Molecules of life”

Answer 23

Two or more atoms held together by covalent bonds

Examples: Oxygen(O₂₎, H₂

Carbohydrates

Lipids

Proteins

DNA

RNA

Question 24

Valence Electrons and Covalent Bonds

How many covalent bonds can hydrogen form?

Oxygen?

Nitrogen?

Carbon?

Answer 24

Question 25

What is Electronegativity?

Answer 25

The attraction of a particular atom for the electrons of a covalent bond. The more electronegative an atom is, the more strongly it pulls the shared electrons toward itself.

Question 26

Polar Covalent Bond vs Nonpolar Covalent Bond

Answer 26

In a covalent bond between two atoms of the same element the electrons are shared equally because the two atoms have the same electronegativity. (the tug of war is at a standoff). Such a bond is called a **nonpolar covalent bond.** When an atom is bonded to a more electronegative atom the electrons of the bond are not shared equally. This type of bond is called a **polar covalent bond**.

Question 27

Question 28

Ionic Bond

Answer 28

a bond between ions

Question 29

Ionic Bond

Answer 29

Question 30

Cation vs Anion

Answer 30

A positively charged ion is called a Cation A negatively charged ion is called an Anion Cations and anions attract each other; this attraction is called an ionic bond

Question 31

Hydrogen Bond

Answer 31

when a hyrdogen atom is covalently bonded to an electronegative atom, the hydrogen atom has a partial positive charge that allows it to be attracted to a different electronegative atom nearby. This attraction between a hydrogen and an electronegative atom is called a hydrogen bond. hyrdogen bonds are weak

Answer 32

Answer 33

Answer 34