Chem Review Flashcards
The smallest, most fundamental material components of the human body are
basic chemical elements
Human chemistry includes
organic molecules (carbon-based) and biochemicals (those produced by the body).
Matter
anything that takes up space and has mass.
amount of matter composing an object; remains constant
— differs from the term “weight”; weight varies with the force of gravity (eg. you weigh almost nothing on the moon but your mass remains the same)
Element
is a pure substance that is distinguished from all other matter by the fact that it cannot be created or broken down by ordinary chemical means
Humans are made of what elements
65% O 18% C 10% H 3% N 4% other
Compound
is a substance composed of two or more elements joined by chemical bonds.
Atom
smallest quantity of an element that retains the unique properties of that element
“are the smallest stable units of matter”
An atom of hydrogen is a unit of hydrogen—the smallest amount of hydrogen that can exist
Atoms are made up of even smaller subatomic particles, three types
proton = a unit of energy that carries a positive charge neutron = are particles that have no electrical charge electron = are particles that have a negative charge
What determines the structure of a given object or being
the way atoms combine and interact
Atoms are composed of _____ that determine the structure of an object
subatomic particles
subatomic particle features
- Protons + Neutrons = mass to the atom,
- # protons determines the element.
- Electrons that “spin” around the nucleus at close to the speed of light
- Elections = protons.
- An electron has about 1/2000th the mass of a proton or neutron.
Atomic Number
the number of protons in the nucleus of the atom, identifies the element. Because an atom usually
has the same number of electrons as protons, the atomic number identifies the usual number of electrons as well.
mass number
is the sum of the number of protons and neutrons in its nucleus
Atoms normally contain _________ protons and electrons
equal numbers
How many elements exist naturally
92
isotope
is one of the different forms of an element, distinguished from one another by different numbers of neutrons. (elements whose atoms nuclei contain the same number of protons but a different number of neutrons)
An isotope that contains more than the usual number of neutrons
Heavy Isotrope. These tend to be unstable, and unstable isotopes are radioactive
radioactive isotope
•an isotope whose nucleus readily decays, giving off subatomic particles and electromagnetic energy
•Different radioactive isotopes (also
called radioisotopes) differ in their half-life, the time it takes for half of any size sample of an isotope to decay.
charge of an atom
are electrically neutral # protons = # electrons (positive charge cancels the negative charge and total charge is zero)
electron shell
is a layer of electrons that encircle the nucleus at a distinct energy level.
• electron shells hold eight
electrons except the first shell, which can only hold two
valence shell
•is an atom’s outermost electron shell
•If the valence shell is full, the atom is stable;
meaning its electrons are unlikely to be pulled away from the nucleus by the electrical charge of other atoms.
•If the valence shell is not full, the atom is reactive; meaning it will tend to react with other atoms in ways that make the valence shell full
octet rule
•All atoms (except hydrogen and helium with their single electron shells) are most stable when there are exactly eight
•an atom will give up, gain, or share electrons with another atom so that it ends up with eight electrons in its own valence shell electrons in their valence shell.
•If the valence shell is full, the atom is stable;
meaning its electrons are unlikely to be pulled away from the nucleus by the electrical charge of other atoms.
•If the valence shell is not full, the atom is reactive; meaning it will tend to react with other atoms in ways that make the valence shell full
radioactive isotopes can be used as
“tracers” that are injected into the body to observe an organ’s function; a scanner is used to detect the emitted radiation to determine if function is normal
Carbon 14
it is a radioactive isotope that decomposes towards a more stable form
- – the half-life of a radioisotope is the amount of time it takes for one-half (50%) of the atoms to decay (lose their activity)
- – C14 has a long half-life of 5730 years and is used for dating archeological finds
elements in a column of the table
have the same physical and chemical properties
rows in periodic table indicate
the number of electron shells in each atom
Atomic mass (or weight
the average of the mass (atomic mass) of all its isotopes
An atom becomes an ion when
ion (charged atom) when it gains or loses an electron (has a positive or negative charge)
Are two models of atomic structure
Orbital model
Planetary model
Orbital model
(= electron cloud model) – depicts “probable” regions of greatest electron density by shading
Planetary model
(= electron shell model) – depicts electrons in circular orbitals or shells around the nucleus
-Planetary model is outdated, however it is still used (in your text) as it is easier to visualize the electrons in their shells
bond
a weak or strong electrical attraction that holds atoms in the same
vicinity
molecule
A more or less stable grouping of two or more atoms held together by chemical bonds
chemical compound
When a molecule is made up of two or more atoms of different elements
Three types of chemical bonds
ionic bonds, covalent bonds, and hydrogen bonds
ion
An atom that has an electrical
charge—whether positive or negative
cation
A positively charged ion
Ex: A potassium ion is written K+, indicating that it has lost a single electron
• Atoms that have more than one electron to donate or accept will end up with stronger positive or negative charges
• A cation that has donated two electrons has a net charge of +2. Using magnesium (Mg) as an example, this can be written Mg++ or Mg2+.
anion
A negatively charged ion
ex: The ionized form of fluorine is called fluoride, and is written as F–.
ionic bond
an ongoing, close association between ions of opposite charge
- covalent bond formed by the transfer of electrons from one atom to another eg. NaCl
- recall, that atoms form ions when they gain or lose electrons
- an atom that loses an electron is an electron donor and has a net positive charge (is a cation)
- an atom that gains an electron is an electron acceptor and has a net negative charge (an anion)
- oppositely charged ions attract and stay together to form an ionic bond
inert
meaning chemically unreactive element due to already having a full valence shell
covalent bond
- molecules share electrons in a mutually stabilizing relationship.
- occurs when two or more atoms share eletrons to form compounds.
- the atoms do not lose or gain electrons permanently.
- Instead, the electrons move back and forth between the elements.
- Because of the close sharing of pairs of electrons (one electron from each of two atoms), covalent bonds are stronger than ionic bonds.
Nonpolar Covalent Bonds
•e-’s shared equally between atoms
•These are stable
• no region of the molecule is either more positive or more negative than any other.
•In a single covalent bond, a single electron is shared between two atoms H-H, while in a double covalent
bond, two pairs of electrons are shared between two atoms O=O. There even are triple covalent bonds, where three atoms are shared.
Polar Covalent Bonds
• e-’s not shared equally between atoms
• a polar molecule is a molecule that contains regions that have opposite electrical charges. Polar molecules occur when atoms share electrons unequally, in polar covalent bonds.
Ex: Water, a nucleus that contains eight protons exerts a charge eight times greater than a nucleus that contains one proton. This means that the negatively charged electrons present in the water molecule are more strongly attracted to the oxygen nucleus than to the hydrogen nuclei. Each hydrogen atom’s single negative electron therefore migrates toward the oxygen atom.
•These charges are often referred to as “partial
charges” because the strength of the charge is less than one full electron,
hydrogen bond
is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for
example, the oxygen in the water molecule) is attracted to another electronegative atom from another molecule. In other words, hydrogen bonds always include hydrogen that is already part of a polar molecule.
- formed when a hydrogen atom with a partial positive charge attracts the partial negative charge of a nearby electronegative atom (most often N or O)
- form between different parts of large molecules such as DNA and proteins
- are weak bonds
Ex: Water, hydrogen bonding occurs because
the weakly negative oxygen atom in one water molecule is attracted to the weakly positive hydrogen atoms of two other water molecules
kinetic energy
is the form of energy powering any type of matter in motion
Chemical energy
• the form of potential energy in which energy is stored in chemical bonds
• When those bonds are formed, chemical energy is invested,
and when they break, chemical energy is released
• Chem energy is not created or destroyed
Potential energy
• is the energy of position, or the energy matter possesses because of the positioning or structure of
its components.
• If the brick wall collapses, the stored potential energy is released as kinetic energy as the bricks fall.
Chemical reactions that release more energy than they absorb are
exergonic
chemical reactions that absorb more energy than they
release are
endergonic
Mechanical energy,
- is stored in physical systems such as machines, engines, or the human body, directly powers the movement of matter.
- When you lift a brick into place on a wall, your muscles provide the mechanical energy that moves the brick.
Radiant energy
- is energy emitted and transmitted as waves rather than matter
- The full spectrum of radiant energy is referred to as the electromagnetic spectrum
Electrical energy,
• supplied by electrolytes in cells and body fluids, contributes to the voltage changes that help transmit impulses in nerve and muscle cells
reactant
one or more substances that enter into the reaction.
Ex: Sodium and chloride ions are the reactants in the production of table salt.
product
one or more substances produced by a chemical reaction
synthesis reaction
is a chemical reaction that results in the synthesis (joining) of components that were formerly separate
A + B → AB.
Ex: N + 3H → NH3
decomposition reaction
is a chemical reaction that breaks down or “de-composes” something larger into its constituent parts
AB → A + B
exchange reaction
• is a chemical reaction in which both synthesis and decomposition occur, chemical bonds are both
formed and broken, and chemical energy is absorbed, stored, and released
• Reversibility is also a quality of exchange reactions
A + BC → AB + C
AB + CD → AC + BD
AB + CD → AD + BC
Chemical Reactions Properties
• Total mass of the reactants = total mass of the products
• Number of atoms of each element stays the same
• Chemical reactions are reversible (occur in either direction)
- however most biological reactions show little tendency to go in reverse
• It is the interactions of valence electrons that are the basis for all chemical reactions - - atoms/molecules are in constant motion (more so in liquids and gases) and they need to collide forcefully to make or break chemical bonds - - takes energy to start the reaction
What is energy
Energy is the capacity to do work
Temperature and chemical reactions
Nearly all chemical reactions occur at a faster rate at higher temperatures
Concentration and Pressure and Chemical Reactions
chemists can speed up chemical reactions not only by increasing the concentration of particles—the number of particles in the space—but also by decreasing the volume of the space, which would correspondingly increase the pressure
catalyst
is a substance that increases the rate of a chemical reaction without itself undergoing any change
enzyme
is a catalyst composed of protein or ribonucleic
acid (RNA)
•Most imporatnt catalyse in the human body
•enzymes work by lowering the level of
energy that needs to be invested in a chemical reaction
activation energy
the “threshold” level of
energy needed to break the bonds in the reactants
Oxidation-reduction reactions
- decomposition reactions which produce ATP from food molecules
- are also a type of exchange reaction as electrons are transferred between atoms and molecules
What influences the speed of chemical reactions?
- An increase in temperature increases the kinetic energy of particles and increases the force of collisions between atoms/molecules as they move faster
- An increase in the concentration of reactants will increase the chance of successful collisions
- A decrease in particle size will increase molecular speed (particles move faster) and increase the reaction rate
- Presence of a catalyst (enzyme) lowers the energy needed to start the reaction so speeds up the process
