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2.2 Molecules and Compounds
The number of electrons in an atom's valence shell determines whether the atom gives up, accepts, or shares electrons to the outer shell.
There are different types of bonds between elements.
A molecule has at least two different elements.
In practice, these two terms are used the same way, but in biology they are usually used in different ways.
H2O is a molecule of hydrogen and oxygen.
The bonds between atoms have energy as well.
Organisms rely on chemical-bond energy to survive.
The organisms break down the sugar to get energy.
When a chemical reaction occurs, electrons shift in their relationship to one another, and energy is released.
Spontaneous reactions always release energy.
Na has one electron in its valence shell and is an electron donor.
The second shell, with its stable configuration of eight electrons, becomes the outer shell when it gives up an electron.
Chlorine is an electron acceptor.
If it only acquires one electron, it has a stable outer shell.
An electron is transferred from the sodium atom to the chlorine atom when there is a chlorine atom.
Both atoms have electrons in their outer shells.
The chlorine atom has an electron transferred from the sodium atom.
Each atom has eight electrons in the outer shell, but it also carries a charge.
In a sodium chloride crystal, ionic bonding between Na+ and Cl- causes the atoms to assume a three-dimensional lattice in which each sodium ion is surrounded by six chloride ions.
The result is crystals of salt.
The sodium atom has a net charge of + after giving up an electron.
The chlorine atom has a net charge of -1 because it has one more electron than it has protons.
The charged particles are called ion.
There are other biologically important ion, such as Na+) and chloride.
Some are formed by the transfer of a single electron to another atom, while others are formed by the transfer of two electrons.
NaCl results when chlorine reacts with sodium.
There is a salt.
Table salt is used to season food.
A result is when two atoms share electrons in a way that each atom has an octet of electrons in the outer shell.
When there are two electrons in a hydrogen atom, the outer shell is complete.
If hydrogen is in the presence of a strong electron acceptor, it becomes a hydrogen ion.
If this is not possible, hydrogen can share with another atom and have a finished outer shell.
The electrons are shared between the two electron shells.
Each atom has an outer shell because they form a bond and share an electron pair.
There are covalently bonding molecules.
Each atom can have a completed outer shell in a covalent bond.
Two hydrogen atoms share a pair of electrons in a molecule of hydrogen.
There are three ways in which this bond can be shown.
There are two pairs of electrons in a molecule of oxygen.
A molecule of methane has one carbon atom and four hydrogen atoms.
Drawing a line between the two atoms is a more common way to symbolize that atoms are sharing electrons.
Just as a handshake requires two hands, one from each person, a covalent bond between two atoms requires two electrons, one from each atom.
Some atoms share more than one pair of electrons.
A double covalent bond is formed when two atoms share electrons.
The molecule can be written as OO to show that it has a double bond.
Nitrogen gas (N2), which can be written as N[?
]N, is possible for atoms to form triple covalent bonds.
Double and triple bonds are even stronger than single bonds.
One atom is able to attract more electrons than the other.
The shape of a molecule can affect whether it is polar or non polar.
While carbon is larger and has more protons than a hydrogen atom, the symmetrical nature of a methane molecule cancels out any polarities.
Water is polar because the oxygen atom is more negative than the Page 27 hydrogen atoms.
Water is a polar molecule because of its nonsymmetrical shape.
The more positive end of the molecule is designated slightly positive.
There are other polar molecule in living organisms.
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