Introduction To Chemistry

Start with Atoms Key Concept Atoms and Elements

An element is a fundamental substance made of one type of atom. The atom is the smallest unit

of an element that still retains the element’s properties.

its building blocks are protons, electrons, and neutrons. Isotopes are atoms of an

element that vary in the number of neutrons.

Start With Atoms An element is a

fundamental substance made up of only ONE KIND of atom.

Atoms are built from three subatomic particles: Protons Neutrons Electrons

Start With Atoms

Protons Protons carry a

positive charge. The symbol of

protons is p+ . Protons will be in the

nucleus of an atom. The atomic number

of each element indicates the number of protons present!

Atomic Number

This element, Neon, has 10 protons!

Start With Atoms Neutrons

Neutrons don’t have ANY charge.

Neutrons are located in the nucleus of the atom.

Neutrons contribute to the atomic mass of the atom! To figure out the number

of neutrons, simply subtract the atomic number from the atomic mass.

When an atom has an unusual amount of neutrons, it becomes an isotope.

Atomic Number

Atomic Mass10-20.2 = 10.2 neutrons

Start With Atoms Electrons

Have a negative charge. The symbol for electrons

is e- . Electrons float around the

atom in several clouds or shells.

The number of electrons equals the number of protons in the atom. The positive charge of

protons and the negative charge of electrons balance each other out in a BALANCED and NORMAL atom. When either protons or

electrons outnumber the other, then the atom becomes an ion.

This element, Neon, has 10 protons AND 10

electrons.

Start With Atoms The number of protons,

electrons, and neutrons in an element predicts their behavior under a variety of conditions inside and outside the body. In 1869, Dmitry Mendeleev

arranged the known elements in a repeating pattern, based on their chemical properties. He used gaps in his periodic

table to correctly predict what elements had not yet been discovered!

Dmitry Mendeleev only cut his hair

once a year!

Periodic Table Elements fall into

order in the table according to their atomic number. All elements in each

vertical column have the same number of electrons that are available for interaction with other atoms. As a result, they behave in similar ways.

Any elements after atomic number 92 are extremely unstable. Some have been

formed in exceedingly small quantities in laboratories.

Putting Radioisotopes To Use Key Concept Why Electrons Matter

Atoms acquire, share, and give up electrons. Whether one atom will bond with others depends on the number and arrangement of its electrons.

Putting Radioisotopes To Use Most naturally occurring elements

have isotopes. Isotopes are one of two or more

atoms of the same element (same number of protons) that differ in their number of neutrons. Carbon has three isotopes, nitrogen

has two, and uranium has fifteen isotopes!

A superscript number to the left of an element’s symbol is the isotopes mass number. 12C = carbon with 6 protons and 6

neutrons 13C = carbon with 6 protons and 7

neutrons 14C = carbon with 6 protons and 8

neutrons

Putting Radioisotopes To Use Some isotopes are unstable, or

radioactive. They are called radioisotopes. A radioisotope will spontaneously emit

energy in the form of subatomic particles and x-rays when its nucleus disintegrates. This process is called radioactive decay,

and it can transform one element into another. Ex. 13C and 14C are radioisotopes of carbon.

Each predictably decays with a particular amount of energy into a more stable product. After 5,700 years, about half of the atoms in

a sample of 14C will have turned into 13N (nitrogen) atoms.

Researchers use radioactive decay to estimate the ages of rocks and biological remains.

Putting Radioisotopes To Use Different isotopes of an element are still

the same element. For the most part, carbon is carbon,

regardless of how many neutrons it has and living systems use 12C the same way as 14C.

Researchers and clinicians who want to track a particular substance can use a tracer. Tracers are molecules in which a radioisotope

has been substituted for a more stable isotope. They can be delivered into a cell or a

multicelled body and can be used to track the pathway or destination of a substance of interest with the help of radioactivity-detecting instruments.

Researchers had plants take up radioactive gas (carbon dioxide made with 14C) and tracked the radioisotope through steps by which plants produce simple sugars and starches.

Putting Radioisotopes To Use PET (Positron-Emission

Tomography) uses radioisotopes to study metabolism. Clinicians attach a radioisotope

to glucose or another sugar and inject it into a patient who is moved into a PET scanner. Cells in different parts of the body

absorb the tracer at different rates. The scanner detects radiation

caused by energy from the decay of the radioisotope and uses it to form an image on a monitor.

Such images reveal variations and abnormalities in metabolic activity.

What Happens When Atoms Bonds with Atom? Key Concept Atoms Bond

The bonding behavior of biological molecules starts with the number and arrangement of electrons in each type of atom. Ionic, covalent, and hydrogen bonds are the main categories of bonds between atoms in biological molecules.

What Happens When Atoms Bonds with Atom?

Electrons in an atom are arranged in orbitals, or volumes of space around the atomic nucleus. These orbitals are called electron clouds, electron shells, or energy levels. Each shell has a specific amount of space

that electrons can occupy. The shell closest to the nucleus of the

atom (the first shell or 1s) can hold up to TWO electrons. This shell has the lowest energy.

The second shell (2s) can hold up to EIGHT electrons.

The third shell (3s) can hold up to EIGHT electrons.

From Atoms To Molecules Atoms with vacancies in their

outermost shell tend to give up, acquire, or share electrons. Chemical bonds are atoms sharing

their electrons with each other. A molecule is simply two or more

atoms of the same or different elements joined in chemical bond.

Compounds are molecules that consist of two more different elements in proportions that never vary. Water is an example.

All water molecules have one oxygen bonded to two hydrogen atoms—H2O

Carbon has 4 e- in its outermost shell. As the third shell can have up to 8 e-, carbon can bond with FOUR other elements.

Hydrogen has 1 e- in its outermost shell. As the first shell can have up to 2 e-, hydrogen can bond with 1 other element.

Ion Formation And Ionic Bonds When an atom contains as

many electrons as protons, these charges balance each other, so the atom has a net charge of zero. When an atom gains an extra

electron, it acquires a net negative charge—It becomes a negative ion

When an atom loses an electron, it acquires a net positive charge-it becomes a positive ion

When a positively charged ion attracts a negatively charged ion, the two associate closely with one another-- this is an ionic bond.

Cl has 7 p+ in its outermost shell and tends to grab e- from someplace else, making it negative Cl-.

Na has 1 e- in its outermost shell and tends to lose it, making it positive Na+

Cl- and Na+ attract and form NaCl or table salt.

Covalent Bonding If both atoms have room for an

extra electron, they can share one in a hybrid orbital that spans both atomic nuclei. When atoms share an electron they

are joined in a single covalent bond. Covalent bonds are stable and are

much stronger than ionic bonds. In a nonpolar covalent bond, two atoms

are sharing electrons equally, so the molecule shows no difference in charge between the two ends.

In a polar covalent bond, two atoms do not share electrons equally which results in one side being more negative than the other. This is called electronegativity.

The O is slightly

negative

The H’s are slightly positive

Both H’s are sharing the e-

equally

Hydrogen Bonding A hydrogen bond is a weak

attraction that has formed between a covalently bound hydrogen atom and an electronegative atom. Because H bonds are weak, they

form and break easily. Collectively, however, many

hydrogen bonds contribute to the properties of liquid water, and play important roles in the structure and function of biological molecules. Many of these bonds hold DNA’s two

nucleotide strands together.