BIO104- Chapter 3

exam 1 - 9/26

Matter

any material that takes up space

element

a substance that cannot be broken down into other substances by chemical means

Atoms

make up all ,atter

Three smaller particles an atom is composed of

protons, neutrons, and electrons

What are protons, neutrons, and electrons?

Subatomic particles

What surrounds the atomic nucleus?

electrons

What are in the atomic nucleus? (center of the atom)

protons and neutrons

subatomic particles are…

electrically charged

What are ions?

charged atoms

How are ions formed?

when an atom either gains or loses electrons

Why is hydrogen ion positively charged?

because it has lost an electron and is left with its one proton

What determines the atomic number?

how many protons are in each atom of that element

What determines the atomic mass?

the total number of protons and neutrons in its atomic nucleus

What is the average mass?

atomic weight

isotopes

different forms of the same element

* same atomic number, different atomic mass

The number of ________ may vary among atoms of the same element

neutrons

Why does each isotope of an element have a different mass?

the number of neutrons differ

What is interesting about isotopes?

they are chemically the same so they behave and are used in organisms the same way

What can radioactive carbon-14 do?

can be used in photosynthesis to make sugars and build plant and animal bodies

What do chemical bonds do?

link atoms together

Molecules are…

two or more chemically joined atoms

What determines chemical bonding

the number and distribution of electrons around an atom determine whether and how the atom will react with other atoms

energy shells (orbitals)

* contain the atom’s electrons
* shells exist at various distances from the atom’s nucleus
* the shell farthest from the nucleus is important for bonding

pure elements

rarely exist - most atoms are connected to others

first electron shell

contains a maximum of 2 electrons

next shells

contain a maximum of 8 electrons

octet rule

atoms want to have full shells to be stable

unpaired electrons

form bonds with other atoms

When are atoms more stable?

when their outer shells have no vacancies

Vacancies

make the atom less stable and more likely to bond with other atoms

Covalent bonds

one or more pairs of electrons are shared by 2 atoms

electronegativity

* measures an atom’s ability to attract electrons
* higher values represent a stronger pull of the nucleus on the electrons
* like the strength of a magnet: some atoms have a stronger pull to keep electrons close

atoms with low electronegativity…

attract electrons weakly

atoms with high electronegativity…

attract electrons strongly

What do atoms with similar electronegativity form?

non-polar covalent bonds

Which atoms have vastly different electronegativity?

Na (low) & Cl (high)

Very electronegative atoms can take…

electrons

Ionic bonds

one or more electrons from one atom are removed and attached to another atom - bonding is formed by association of positive and negative charged (weaker than covalent bonds)

Some atoms have __________ electronegativity

different

Polar covalent bonds

one or more pair of electrons are shared by two atoms - but atoms have different electronegativities pulling electrons closer to one atom over another

Hydrogen bonds

a weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom in the other

T or F: Oxygen is one of the least electronegative elements

False: it is one of the most electronegative

________ bonds pull water molecules close to each other

hydrogen

Cohesion

the tendency of water molecules to stick to one another

(water is cohesive)

Adhesion

bonds to surfaces

(water is adhesive)

How is water cohesive and adhesive?

together, cohesion and adhesion allow water molecules to “climb” from a tree’s roots to its highest leaves

What does water dissolve?

* polar solutes
* ions
* salt (NaCl)
* sugars

What makes water resist changes in temperature?

hydrogen bonds

T or F: Water cools and heats up very slowly

true

What do hydrogen bonds lead to?

* high specific heat- large amounts of energy required to change temp
* makes it liquid over a wide range of temperatures
* high heat of vaporization- similar large amount of energy to convert from liquid to gas phase
* provides heat loss to surfaces on phase change (evaporation)