2.1 The Building Blocks of Molecules

Life is made up of matter.

Each element has a constant number of protons and unique properties.
A total of 118 elements have been defined, but only 92 are naturally occurring and less than 30 are found in living cells.
The unstable elements do not exist for very long or have yet to be detected.

The chemical symbol for each element is H, N, O, C, and Na.

The unique properties allow elements to bond in different ways.

All of the chemical properties of an element are retained by an atom.

One hydrogen atom has all of the properties of the element hydrogen, such as it being a gas at room temperature, and it bonds with oxygen to create a water molecule.
The properties of hydrogen cannot be broken down into smaller atoms.
The properties of hydrogen would be lost if a hydrogen atom were broken down.

All organisms are made of a combination of elements.

They contain atoms that are 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- 888-609- Molecules can interact to form cells that combine to form tissues in multicellular organisms.
Until multicellular organisms are formed, these combinations continue.

The atoms are made of protons, electrons, and neutrons.

It resides outside of the nucleus.
It has a small mass and a small charge.

The nucleus contains protons and neutrons, and electrons surrounding it.

There is a mass of 1 and no charge.

The neutral atom has a net zero charge because the positive and negative charges balance each other.

The number of protons and neutrons in an atom is equal to the mass of the atom.

The mass of the electrons is so small that they don't factor into it.

Each element has its own unique properties.

Each has its own atomic number and mass number.

The number of neutrons can be determined by subtracting the atomic number from the mass number.

Information about the elements and how they will react is provided by these numbers.

Different elements have different melting and boiling points, and are in different states at room temperature.
They combine in different ways.
Some form bonds that are specific, while others do not.
The number of electrons is what determines how they combine.
The periodic table has information about the properties of elements.
The arrangement of the table shows how the electrons in each element are organized and provides important details about how atoms will react with each other to form a molecule.

There are elements that have naturally occurring isotopes.

Carbon-12 has six protons and six neutrons.
It has a mass number of 12 and an atomic number of 6.
The element carbon has a mass number of 14 and an atomic number of 6.
There are two different forms of carbon.
Some of the elements are unstable and will lose protons, other particles, or energy to form more stable elements.

The periodic table has rows and columns based on the characteristics of the elements.

A key or legend is provided to the information in periodic tables.

Cosmic rays create carbon-14 (14C) in the atmosphere.

More 14C is always being created.
The relative level of 14C in the body is the same as the concentration in the atmosphere.
The ratio will decline when an animal dies.
14C decays to 14N through a process called beta decay.

Only half of the starting concentration of 14C will be converted to 14N.

Half-life is the time it takes for half of the original concentration to decay to its more stable form.
Because the half-life of 14C is long, it is used to age fossils.
The ratio of the 14C concentration found in an object to the amount of 14C detected in the atmosphere can be used to determine the amount of decay.
The age of the fossil can be calculated to about 50,000 years based on this amount.
Scientists can reconstruct the ecology and biogeography of organisms using carbon dating.

Carbon dating can be used to determine the age of remains that are less than 50,000 years old.

How elements interact with one another depends on how their electrons are arranged and how many openings there are for electrons in an atom.

The shells around the nucleus are formed by electrons.
The closest shell can hold up to two electrons.
The closest shell to the nucleus is always filled first.
Hydrogen has one electron and only one spot in the lowest shell.
Helium can fill the lowest shell with its two electrons.
There are only two elements in the first row of the periodic table.
They only have electrons in their first shell.
The two elements that have the lowest shells are hydrogen and helium.

Up to eight electrons can be held by the second and third energy levels.

The electrons are arranged in four pairs and one position in each pair is filled with an electron before any pairs are completed.

There are seven rows in the periodic table.

The number of shells in the row correspond to these rows.
As the columns move from left to right, the elements within a row increase in number of electrons.
Although each element has the same number of shells, not all of them are completely filled with electrons.
If you look at the second row of the periodic table, you will find a lot of things.
The first and second shells are the only ones with electrons.
When the entire shell is filled with eight electrons, as is the case with neon, there is only one electron in the outermost shell.

When all of the electron positions in the outermost shell are filled, an atom is at its most stable.

To achieve greater stability, atoms will fill their outer shells and bonds with other elements by sharing electrons, donating electrons to another atom, or accepting electrons from another atom.

The octet rule requires elements to fill their outer shell with electrons from other elements.

Each ion has a net charge because the number of electrons doesn't match the number of protons.

sodium has one electron in its shell.

It takes less energy for sodium to donate one electron than it does to accept seven more.
If sodium loses an electron, it now has 11 protons and only 10 electrons, leaving it with an overall charge of +2.
It's now called a sodium ion.

There are seven electrons in the chlorine atom.

It is more efficient for chlorine to gain one electron than to lose seven.
The net negative charge is caused by it gaining an electron to create an ion with 17 protons and 18 electrons.
It's now called a chloride ion.
A chlorine atom has seven electrons in its outermost shell, whereas a sodium atom only has one electron.
A chlorine atom will accept an electron from a sodium atom to fill it's shell.
Both ion have complete outer shells.
Because the number of electrons is no longer equal to the number of protons, each is an ion and has achloride charge.

The elements fill their shells with electrons.

They can either accept electrons from other elements or donate them.

Van der Waals interactions are one of the four types of bonds.

The bonds need a larger energy input to break apart.
A positive ion is formed when an element donates an electron from its outer shell.
The element is no longer accepted by the electron.
The elements bond with the electron from one element to another.
An electron from a sodium atom stays with the other seven from the chlorine atom, and the chlorine and Na+ ion attract each other in a lattice of ion with a net zero charge.

The strongest and most common form of chemical bond in living organisms is when an electron is shared between two elements.

The elements in our cells form bonds.
covalent bonds are not in water.

The hydrogen and oxygen atoms are bound together by bonds.

The incomplete outer shell of the oxygen atom is divided by an electron from the hydrogen atom.
Two electrons from two hydrogen atoms are needed to fill the outer shell of an oxygen atom.
The electrons are split between the atoms and used to fill the outer shell.
If all of the atoms were filled with their outer shells, this sharing would have a higher energy state for them.

There are two types of bonds.

An oxygen atom can bond with another oxygen atom to fill their shells.
The electrons will be distributed between each oxygen atom.
Oxygen requires two electrons to fill its shell and two bonds form between the two oxygen atoms.
Each nitrogen atom needs three electrons to fill its shell, so triple covalent bonds are formed between two nitrogen atoms.
There is a nonpolar bond in the methane molecule.
Four more electrons are needed to fill the carbon atom's shell.
Each hydrogen atom gives one of these four.

A slightly positive or slightly negative charge develops because of the distribution of electrons.

Water has polar covalent bonds between hydrogen and oxygen atoms.
electrons spend more time near the oxygen nucleus, giving it a small negative charge, than they spend near the hydrogen nucleus, giving these molecule a small positive charge.

The water molecule has a positive charge on the hydrogen atoms and a negative charge on the oxygen.

Oxygen and methane are examples of nonpolar bonds.

Strong bonds require a lot of energy to break.

Some bonds between elements are not ionic or covalent.
aker bonds can be formed.
Positive and negative charges do not require much energy to break these attractions.
Van der Waals interactions and hydrogen bonds are weak bonds that occur frequently.
The bonds give rise to the unique properties of water.

The hydrogen atom in a polar covalent bond has a slightly positive charge.

The shared electron is pulled away from the hydrogen nucleus.

The hydrogen atom will be attracted to neighboring negative partial charges if it is positive.

There is a weak interaction between the d+ charge of the hydrogen atom of one molecule and the d- charge of the other molecule.
The liquid nature of water is caused by the hydrogen bonds between water molecule.
Water has unique properties that sustain life.
Water would be a gas if it weren't for hydrogen bonding.

Water can not always be included in hydrogen bonds.

Hydrogen atoms can form bonds with other Molecules.
The double-stranded structure of the DNA molecule is due to hydrogen bonds holding together two long strands of the molecule.
Some of the three-dimensional structure of proteins is caused by hydrogen bonds.

They occur between polar and covalently bound atoms.

The weak attractions are caused by partial charges formed when electrons move around a nucleus.
Weak interactions between Molecules are important in biological systems.