Ap bio chp 2

2 and 3 are the same test but i split them

Atomic number

– number of protons in an atom of a particular element.

Mass number

– number of protons and neutrons in an atom.

Calculate the number of neutrons by

subtracting atomic number from mass number

In a neutral atom,

# protons = # electrons.

Number of neutrons can vary in an element, but the number of protons

is constant

Isotopes

– atoms of an element that have the same atomic number but different mass number.

(Isotopes) They have the same number of protons, but

a different number of neutrons.

Valence

– bonding capacity of an atom which is the number of covalent bonds that must be

formed to complete the outer electron shell.

Valences of some common elements:

hydrogen = 1,

oxygen = 2, nitrogen =3, carbon = 4, phosphorus = 3 (sometimes 5 as in biologically important

compounds (ATP), sulfur = 2.

Electronegativity

– atom’s ability to attract and hold electrons, the more electronegative an atom,

the more strongly it attracts shared electrons.

valence shell is complete when

it contains eight electrons (except H and He).

An atom with a complete valence shell is

unreactive or inert.

Noble elements (helium, argon, and neon) have filled outer shells in their elemental state and

are

thus inert.

Trace elements

– element required by an organism in extremely minute quantities.

(Trace elements) example

I, Fe

Atoms are made up of

subatomic particles.

Neutrons

No charge, Found together in a dense core called the nucleus,1.009 dalton (mass),(positively charged because of protons)

PROTONs

+1 charge, Found together in a dense core called the nucleus,1.007 dalton

ELECTRON

-1 charge, Orbits around the nucleus (held by electrostatic attraction to positively

charged nucleus), 1/2000 dalton

an atom is electrically neutral, the number of protons equals

the number of electrons,

true or false: an atom may gain or lose electrons but the number of protons in an atom never changes

true

Ion

charged atom or molecule.

What is the difference between a neutral atom and an ion of same element?

A neutral atom has an equal number of protons and electrons (zero charge), while an ion has gained or lost electrons, giving it a positive or negative charge.

What is the difference between a neutral an element's valence electrons and its valence number?

Valence electrons are the actual number of electrons present in an atom's outermost energy shell (the valence shell).

Valence number (or simply valence) is an atom's bonding capacity. It represents the number of covalent bonds an atom must form in order to complete its outer electron shell

(valence electrons and valence number) example

Oxygen has 6 valence electrons in its outer shell, but its valence number is 2 because it needs to form 2 bonds to complete its shell with 8 electrons.

The first electron shell can hold electrons while all the other shells can hold __ electrons.

The first electron shell can hold 2 electrons while all other shells can hold 8 electrons.

First shell:

Contains one spherical s orbital (1s orbital) that holds a maximum of 2 electrons

Other shells:

Hold up to 8 electrons across one s orbital and three p orbitals, satisfying the octet rule for chemical stability.

what is the difference between a covalent bond and an ionic bond

Covalent Bond: Atoms share electrons to stay connected. This forms a strong bond that stays intact in water. Example: Water - H₂O

Ionic Bond: One atom gives away an electron, and another takes it, creating opposite charges that attract. This bond is strong when dry but breaks apart easily in water. Example: Table salt (NaCl).

What is the difference between a polar covalent bond and a nonpolar covalent bond?

Nonpolar Covalent Bond: Atoms share electrons equally. Because the electrons stay centered, neither side gets a charge. Example: Methane (CH₄) or oxygen gas (O₂)

Polar Covalent Bond: Atoms share electrons unequally because one atom pulls harder on them. This gives the greedy atom a slight negative charge (-) and the other atom a slight positive charge (+). Example: Water (H2O).

Matter

anything that has mass and takes up space.

Mass

– a measure of the amount of matter an object contains and it stays the same regardless of

changes in the object’s position.

Element

– a substance that cannot be broken down into other substances by chemical reactions.

About 25 of the 92 naturally occurring elements are essential to life. Biologically important

elements include:

C = carbon

O = oxygen

H = hydrogen

N = nitrogen all make up 96% of all living matter

Compound

a pure substance composed of two or more elements combined in a fixed ratio.

b. Example: NaCl (sodium chloride)

(compound) example

Has unique emergent properties beyond those of its combined elements (Na and Cl have very

different properties from NaCl).

atom

smallest possible unit of matter that

retains the physical and chemical properties of its element. Atoms of the same element share similar

chemical properties.

electrons

light negatively charged particles that orbit around the

nucleus,

Energy

– ability to do work

Potential energy

energy that matter stores because of its position or location.

Different fixed potential energy states for electrons are called

energy levels or electron shells

Electrons with lowest potential energy are in energy levels

closest to the nucleus.

Electrons with greater energy are in energy levels

further from the nucleus.

Electron orbital

– three-dimensional space where an electron will most likely be found 90% of the

time

An atom’s electron configuration

– distribution of electrons in an atom's electron shells,

determines its chemical behavior.

Chemical properties of an atom depend upon the number of valence electrons

electrons in the

outermost energy shell (valence shell).

Octet rule

– valence shell is complete when it contains eight electrons (except H and He).

An atom with a complete valence shell is

unreactive or inert.

An atom with an incomplete valence shell is

chemically reactive (tends to form chemical

bonds until it has eight electrons to fill the valence shell). Atoms with the same number of

valence electrons show similar chemical behavior.

chemical bonds

– attractions that hold molecules together.

Covalent bonds

– chemical bond between atoms formed by sharing a pair of valence electrons.

Structural formula

- formula which represents the atoms and bonding within a molecule (H-H).

The line represents a shared pair of electrons.

Molecular formula

– formula which indicates the number and type of atoms (H2).

Single covalent bond

– bond between atoms formed by sharing a single pair of valence electrons,

atoms may freely rotate around the axis of the bond.

Double covalent bond

bond formed when atoms share two pairs of valence electrons (O2).

Molecules

two or more atoms held together by chemical bonds.

Triple covalent bond

bond formed when atoms share three pairs of valence electrons (N2)

Double and triple covalent bonds are

rigid and do not allow rotation.

Nonpolar covalent bond

– covalent bond formed by an equal sharing of electrons between atoms.

i. Occurs when electronegativity of both atoms is about the same (CH4)

Polar covalent bond

covalent bond formed by an unequal sharing of electrons between atoms.

(Polar covalent bond) Occurs when the atoms

involved have different electronegativities. Shared electrons spend more time around the more electronegative atom. In H2O, for example, the oxygen is strongly electronegative, so negatively charged electrons

spend more time around the oxygen than the hydrogens.

Ion

charged atom or molecule.

Anion

– an atom that has gained one or more electrons from another atom and has become

negatively charged; a negatively charged ion.

Cation

an atom that has lost one or more electrons and has become positively charged; a

positively charged ion.

Ionic bond

bond formed by the electrostatic attraction after the complete transfer of an electron

from a donor atom to an acceptor. strong bonds in crystals, but are fragile bonds in water;

ionic bonds help stabilize

the three-dimensional shape of large molecules (DNA and proteins).

Hydrogen bonds

bond formed by the charge attraction when a hydrogen atom covalently bonded to

one electronegative atom is attracted to another electronegative atom. Is a charge attraction between oppositely charged portions of polar molecules

Van der Waals interactions

weak interactions that occur between atoms and molecules that are

very close together and result from charge asymmetry in electron clouds.

A molecule’s biological function is related to its shape

A molecule has a characteristic size and shape. The function of many molecules depends upon their

shape.

Chemical reactions

process of making and breaking chemical bonds leading to changes in the

composition of matter.

a. Process where reactants undergo changes into products.

b. Matter is conserved, so all reactant atoms are only rearranged to form products.

Chemical equilibrium

– equilibrium established when the rate of forward reaction equals the rate of

the reverse reaction.