2. Chemical Context of Life Flashcards
What is an Element?
An Element is a substance that cannot be broken down to other substances by chemical reactions.
What 4 elements make up 96.3% of our body mass
Oxygen
Carbon
Hydrogen
Nitrogen
How many elements are there in the human body
25
What is a compound?
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
What is an Atom
What is an atom composed of?
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.
Atomic Number =
Atomic Mass =
What is the relation between protons and electrons?
- 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).
Elements are arranged on the periodic table according to the number of _________?
Protons
and since # electrons = # of protons it could also be said that it is arranged by number of electrons
What are Isotopes?
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
What is a Radioisotope
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
What is a Half-life?
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.
Example
The chemical behavior of an atom depends mostly on?
An atom with a completed valence shell is _____?
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.
Electron Shells
How many electrons does the first shell hold?
” “ 2nd Shell holds?
” “ 3rd shell holds?
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
Electron Orbitals
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.
Electron shells vs Electron orbitals
What is a valence shell?
What is a valence electron?
A valence shell is the outermost shell involved in bonding
Valence electrons are the outer electrons involved in bonding
The reactivity of an atom arises from the presence of:
The reactivity of an atom arises from the presence of unpaired electrons in one or more orbitals of the atom’s valence shell.
Exercise: For the three elements provide:
Atomic Number
Atomic Mass
Proton Number
Neutron Number
Electron Number
Electron Shell
Valence Shell
Valence Electron
Why are electron shells and orbitals important?
- Covalent bond
- Ionic bond
- Hydrogen bond
- Van der Waals Interaction
What is a Covalent Bond?
a covalent bond is the sharing of a pair of valence electrons by two atoms
What are Molecules/compounds?
What are the “Molecules of life”
Two or more atoms held together by covalent bonds
Examples: Oxygen(O2), H2
Carbohydrates
Lipids
Proteins
DNA
RNA
Valence Electrons and Covalent Bonds
How many covalent bonds can hydrogen form?
Oxygen?
Nitrogen?
Carbon?
What is Electronegativity?
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.
Polar Covalent Bond vs Nonpolar Covalent Bond
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.
Ionic Bond
a bond between ions
Ionic Bond
Cation vs Anion
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
Hydrogen Bond
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
