Chemistry of Life #6

atoms —> molecules —> organelles —> cells —> tissues —> organs

atoms —> molecules —> organelles —> cells —> tissues —> organs

nucleus

• in the center of the atom

• composed of protons and neutrons 

proton

• positive charge

• define/identify the atom

• atoms with each specific number of protons are different elements

neutron

• neutral (no) charge

electron

• orbit the nucleus & have negative charge

• form a cloud around the nucleus

• they are all negatively charged so they all repel each other into a predictable pattern

orbits

• electrons can move between orbitals if there is space

• electrons can jump to a higher orbital if excited (energy is added) 

• when electrons fall back to a lower orbital, they emit energy

• the further the orbit is from the nucleus, the larger the energy needed/emitted 

Element 

• atoms with each specific number of protons = different ______

atomic mass = # protons + # neutrons 

equation for atomic mass

# protons

atomic number = ?

isotope

• versions of an element that have the expected number of protons and electrons, but more or fewer neutrons than they should have

  • behave identically in chemical reactions

carbon 14

• a rare and radioactive isotope

• used for radiocarbon dating

• naturally created in small quantities in the atmosphere, and incorporated into plant tissues through photosynthesis

  • when we eat plants we take in these rare C14 molecules alongside regular C12 and incorporate them all into our bodies

• C14 decays into nitrogen with a half life of 5,730 yrs 

• when an organisms dies it stops taking this in so we can measure how much is in a dead body to find how long ago it died and therefore when it lived 

Ions 

• when the balance between protons and electrons becomes unbalanced, a atom maintains an electrostatic charge and becomes an ion 

  • cation (+) = lose an electron

  • anion (-) = gain an electron

electron shells

• the physical spaces where electrons are found orbiting around a nucleus 

  • each shell can contain a diff # of electrons

    • 1st shell (closest to nucleus) can hold up to 2 electrons

    • 2nd shell can hold up to 8 electrons

    • 3rd shell can hold up to 18 electrons

    • 4th shell can hold up to 32 electrons

Valence shell

• the outermost shell of an atom’s electron orbit 

• the electrons in this shell are especially important for bonds 

  • they have the weakest attraction to nucleus, so more likely to be influenced by other atoms

Molecule

• when two or more atoms bond, this makes a _____

chemical bonds

• a form of attraction between atoms that holds them together

Covalent bonds

• occur when 2 atoms share valence electrons

• when 2 valence electrons come into proximity, 2 valence shells, each containing one electron, merge into a single shell containing a full complement of two electrons (share the 2 electrons in the 1 molecular orbital)

• diff bonds form depending on ow many electrons are in the valence shell of an atom

single covalent bonds

covalent bond in which 1 electron is shared between atoms 

double covalent bonds

a covalent bond in which 2 electrons are shared between atoms

an atom can only have as many covalent bonds as it has missing electrons in its valence shell

an atom can only have as many covalent bonds as it has missing electrons in its valence shell

polar covalent bonds

• type of covalent bonds that form when electrons are shared unequally between atoms

Ionic bonds

• when the difference in electronegativity between two atoms is really big, one atom steals an electron from the other —> making two ions

  • the 2 charged ion atoms are now drawn together and bonded, but the electrons “belong” to each atom individually & are not shard between the atoms

Hydrogen bonds

• the slight polarity of polar molecules causes them to be weakly attracted to one another

  • the two molecules do not share their electrons, but do “stick” together

Van der Waals (bonds)

• electrons constantly moving around their orbitals & sometimes accumulate in one end of a molecule 

  • this makes the molecule momentarily polar (even if non-polar overall)

  • enables weak inter-molecule attractions similar to hydrogen bonds but much weaker

electronegativity

• the measure of how strongly an atom attracts shared electrons 

  • O is more electronegative than H, so electrons spend more time near O (O has a slight - charge and H has a slight + charge)

Water expansion (upon freezing)

• when water freezes into ice it forms crystals that are shaped and spaced by hydrogen bonds between molecules

  • water molecules pack together tightly / tighter than if in liquid form bc the hydrogen bonds while in liquid form are not in the same order (so when reorder themselves they get closer together)

Water cohesion

• water molecules stick to each other

  • hydrogen bonds make water molecule _____

  • pulls water up the tree as molecules are released into the atmosphere during transpiration

Water adhesion

• water molecules stick to surfaces with a charge

  • hydrogen bonds also make water molecules adhesive

  • adhesion sticks to xylem walls and helps the water molecules work against gravity

specific heat

• the amount of energy that must be absorbed or lost by 1g of a substance to change its temperature by 1C

  • the ______ of the water in your body helps you resist differences in external temperatures

  • water: 1 cal/ (g x C)

Solvent 

• a substance which another substance (the solute) is dissolved in

• the polar nature of water makes it a good _____

  • it is capable of dissolving more substances than any other ____ known

  • water molecules can dissolve any other molecules that has some degree of polarity

  • water cannot dissolve non-polar molecules

hydrophobic 

• molecules that water cannot dissolve

  • non-polar

    • lipids and oils

hydrophilic 

• molecules that water can dissolve

  • polar molecules

extraterrestrial signs of life

• water is vital to life on earth (must be vital to life elsewhere)

  • astro-biologists study other planetary bodies with water to look for signs of extraterrestrial life