BIO 201 CHAPTER 2
What is Matter?
Anything that takes up space and has mass
What is mass?
The amount of matter in an object
What is an element?
A substance that cannot be broken down to other substances by chemical reactions
What is a compound?
A substance consisting of two or more elements in a fixed ratio but has characteristics different from those of its elements
What elements make up 96% of living matter?
Carbon, hydrogen, oxygen, and nitrogen. Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur
Those required by an organism in minute quantities
An atom is?
The smallest unit of matter that still retains the properties of an element
Atoms are composed of subatomic particles such as?
Neutrons (no electrical charge)
Protons (positive charge)
Electrons (negative charge)
What two forms the atomic nucleus?
Neutrons and protons
What does the electron form?
A cloud around the nucleus
What is an element’s atomic number?
The number of protons in its nucleus
What is an element’s atomic mass ?
The sum of protons plus neutrons in the nucleus, the atom’s total mass, can be approximated by the mass number
Two atoms of an element that differ in number of neutrons. All atoms
of an element have the same number of protons but may differ in number
Carbon 12: 6 protons: 6 neutrons
Carbon 13: 6 protons: 7 neutrons
Carbon 14: 6 protons: 8 neutrons
Nucleus that decays spontaneously
Releases particles and energy
Is the capacity to cause change
The energy that matter has because of its location or structure (stored energy)
Negatively charged electrons are attracted to?
Positively charged nucleus (The more distant from the nucleus, the more potential energy)
An electron’s state of potential energy is called its energy level, or electron shell.
Chemical behavior of an atom is determined by the distribution of electrons in electron shells
Are those in the outermost shell, or valence shell
The chemical behavior of an atom is mostly determined by the valence electrons
Elements with a full valence shell are chemically inert
An orbital is?
The three-dimensional space where an electron is found 90% of the
Similar to planets orbiting the sun
Each electron shell consists of a specific number of orbitals
No more than 2 electrons can occupy a single orbital
First shell can accommodate 2
Second can accommodate 8
Electrons in each of these orbitals have the same energy but move in different volumes of space
What happens when orbitals have unpaired electrons in their valence shells?
Atoms become reactive and will form compounds or molecules
Atoms want all of their electrons to be paired
Atoms with incomplete valence shells can share or transfer valence
electrons with certain other atoms
These interactions usually result in atoms staying close together, held by attractions
The sharing of a pair of valence electrons by two atoms
In a covalent bond, the shared electrons count as part of each atom’s valence shell
1 valence electron
2 hydrogen atoms become close, 1s orbitals overlap
Each now has 2 electrons
Consists of two or more atoms held together by covalent bonds
A single covalent bond, or single bond, is the sharing of one pair
of valence electrons
A double covalent bond, or double bond, is the sharing of two pairs of valence electrons
An atom’s attraction for the electrons in a covalent bond
The more electronegative an atom, the more strongly it pulls shared electrons toward itself
Covalent bonds are a tug of war for electrons…
If equally electronegative - nonpolar
Examples: H2 and O2
If the atoms are NOT equally electronegative - polar
Oxygen atoms contain more protons than hydrogen atoms
These protons attract electrons
Electrons spend more time near the oxygen nucleus than the hydrogen nucleus
The oxygen atom has a slightly negative charge
The hydrogen atoms have a slightly positive charge
Is an attraction between an anion and a cation:
Atoms sometimes strip electrons from their bonding partners. They don’t want to share!
A charged atom (or molecule)
Polarity varies depending upon ?
The electronegativity of the atoms
A cation is ?
a positively charged ion (t=+)
An anion is ?
a negatively charged ion
Compounds formed by ionic bonds ( salts)
strongest bonds in organisms
are covalent bonds that form a cell’s molecules
Weak chemical bonds
Ionic bonds and hydrogen bonds, are also important
Weak chemical bonds reinforce shapes of large molecules and help molecules adhere to each other
A hydrogen bond
Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom
Molecules with similar shapes can have ?
Similar biological effects;
Biological molecules recognize and interact with each other with a specificity based on molecular shape
The making and breaking of chemical bonds
The starting molecules of a chemical reaction;
The final molecules of a chemical reaction are called products