Chapter 2 Flashcards
Organisms are composed of matter, which is:
Anything that takes up space and has mass.
An element:
A substance that cannot be broken down to other substances by chemical reactions.
Matter is made up of…
Elements
How many elements are recognized in nature by chemists today?
92
A compound is:
A substance consisting of two or more different elements combined in a fixed ratio
How much of the 92 natural elements are essential for a healthy life and reproduction?
20 to 25%
Trace elements:
Required by an organism in only minute quantities
Atoms:
The smallest unit of matter that still retains the properties of an element.
Adams are composed of even smaller parts called:
Subatomic particles
Each proton has one unit of…
Positive charge
Each electron has one unit of…
Negative charge
Atomic number
The number of protons in the nucleus of a particular element.
Written as a subscript to the left of the symbol for the element.
Mass number:
The number of protons and neutrons in the nucleus of an atom.
Written as a subscript to the left of an element symbol.
The number of neutrons in the nucleus of an atom can be determined by:
Subtracting the atomic number from the mass number
Isotopes
Different atomic forms of the same element.
Stable isotopes
Nuclei do not have a tendency to lose it subatomic particles.
Radioactive isotope
Nucleus decays spontaneously, giving off particles and energy.
Half-life of the isotope:
The time it takes for 50% of the parent isotope to decay.
Energy is defined as:
The capacity to cause change
Potential energy
The energy that matter possesses because of its location or structure
Matter has a natural tendency to move toward the…
Lowest possible state of potential energy
Electrons have potential energy due to their…
Distance from the nucleus
The more distant an electron is from the nucleus, the…
greater its potential energy.
And electrons potential energy is determined by…
Its energy level.
And electron can only exit at certain energy levels, not between them.
An electron can move from one shell to another, but only by…
Absorbing or losing an amount of energy equal to the difference in potential energy between its position in the old shell and that in the new shell.
When an electron absorbs energy:
It moves to a shell farther out from the nucleus
When an electron loses energy:
It falls back to a show closer to the nucleus, lost energy is usually released to the environment as heat.
The chemical behavior of an Atom depends mostly on:
The number of electrons in its outer most shell
Valance electrons
Electrons in the outer shell
Valance shell
The outer most electron shell
Atoms with the same number of electrons in their valance shells…
Exhibit similar chemical behavior
And atom with a completed valance shell is:
Unreactive; will not interact readily with other atoms
Inert
Chemically unreactive
Orbital
The three-dimensional space where an electron is found 90% of the time
Covalent bond
Sharing of a pair of balance electrons by two atoms
Two or more atoms how together by covalent bonds constitute a…
Molecule
Compound
A combination of two or more different elements
Electronegativity
The attraction of a particular Atom for the electrons of a covalent bond.
A nonpolar covalent bond
A covalent bond between two atoms of the same element, electrons are shared equally because the two atoms have the same electronegativity
A polar covalent bond
When an atom is bonded to a more electronegative atom. Electrons are not shared equally.
Ions
The two resulting oppositely charged atom or molecules. Two atoms are so an equal in their attraction for a valance electron is that the more electronegative atom strips an electron completely away from his partner.
A positively charged ion is called
An cation
A negatively charged ion is called
An anion
An ionic bond
Is formed due to the opposite charges, cations and anions which attract each other.
Hydrogen bond
Hydrogen atom is covalently bonded to a electron negative atom, the hydrogen atom has a partial positive charge that allows it to be attracted to a different electronegative atom nearby.
In living cells, the electronegative partners of the partially positive charged hydrogen atom are usually:
Oxygen or nitrogen atoms
