Biol 221 Worksheet

Basic Chemistry

I.Matter

Matter is anything that has ______and occupies ______.

List the three different states as which matter exists, and an example of each found in the human body.

  1. ______, example - ______
  2. ______, example - ______
  3. ______, example - ______

II.Energy

Energy is defined as: ______.

The human body is able to convert energy into three forms; list them:

  1. ______
  2. ______
  3. ______

Name the molecule that serves as a main source of energy for cells: ______

III.Elements

All matter is composed of elements.Elements are unique substances that can’t be broken down into simpler substances by ordinary chemical methods.

The smallest complete unit of an element is called an ______.

Name the four most common elements found in the human body:

  1. ______
  2. ______
  3. ______
  4. ______

A complete listing of elements is found in the ______.

IV.Atoms & Subatomic Particles

Atoms are the smallest units that participate in chemical ______. The atoms of each element are different from the atoms of any other type of element.

Complete the following table:

Subatomic Particle / Location in Atom / Charge / Mass
Positive (+)
Neutron
Almost none

Within an atom, the number of positively charged ______always equals the number of negatively charged ______.

Therefore, the overall charge of an atom is ______.

V. Atomic Number

The Atomic Number of an element is equal to the number of ______in the nucleus of each atom of that element.

Hydrogen has an atomic number of one (1). How many protons in each hydrogen atom? ______

A carbon atom has 9 protons. What is its atomic number? ______

How many electrons does a carbon atom have? ______

If an atom has 92 protons in its nucleus, how many electrons will it have orbiting outside its nucleus? ______

VI. Mass Number

The Mass Number of an element is the sum of the masses of all of the subatomic particles in the atom. We will ignore the mass of electrons, and only consider the mass of the protons and neutrons. So in this course, add up all of the protons and neutrons to find the mass number.

A hydrogen atom has a mass number of ______AMU or daltons.

An oxygen atom has a mass number of ______AMU or daltons.

The number of neutrons can be determined by subtracting the atomic number (# of protons) from its mass number (sum of protons & neutrons).

A carbon atom has an atomic number of 6 and a mass number of 12. How many protons in its nucleus? ______

How many electrons outside its nucleus? ______

How many neutrons in its nucleus? ______

If an atom has a mass number of 51 and an atomic number of 25, how many of each type of subatomic particle does it have?

Protons ______

Electrons ______

Neutrons ______

VII. Electron Orbitals (energy levels)

Electrons are located outside of the atomic nucleus. These electrons make up the electron cloud, which can be divided up into areas called orbitals or shells (or energy levels). Now that you are able to determine the number of electrons in an atom, you should be able to determine the number of ______in each orbital.

Although there is a mathematical formula that can be used, we are going to keep it simple. You only need to determine the number of electrons for the first three orbitals (the three areas closest to the atomic nucleus). Each orbital can hold a certain number of electrons.

The first orbital can hold ______electrons.

The second orbital can hold ______electrons.

The third orbital can hold ______electrons.

The first orbital must be filled with 2 electrons before electrons go into the second orbital.

The second orbital must be filled with 8 electrons before electrons go into the third orbital.

Draw the structure of a silicon atom, atomic number 14 and mass number 28. Include the correct location of all three types of subatomic particles, and place the electrons in the correct orbitals.

VIII.Chemical Bonds

The outermost electrons in an atom are called the valence electrons. The valence electrons determine the atom’s ______, and only the valence electrons participate in a chemical reaction.

The outermost orbital that contains these electrons is called the valence orbital or valence shell. If this outermost orbital contains the maximum number of electrons, or is “full”, the atom is ______and relatively unreactive. However, if the valence orbital is not full, then that atom is unstable and will tend to react with other atoms in such a way that its ______orbital becomes full.

Unstable atoms can gain, lose, or share electrons with other unstable atoms until they become ______. Moving electrons or sharing electrons between atoms results in chemical bonds. Chemical bonds join ______together, forming molecules or ______.

  1. Ionic Bonds

Electrons are negatively charged. So, if an atom loses an electron, the atom will then have an overall ______(negative/positive) charge.

If an atom gains an electron, it will then have an overall ______charge.

An ion is an atom that has acquired a net (overall) charge by either gaining or losing ______.

If a hydrogen atom loses an electron, it becomes a hydrogen ion. Because it lost an electron, it becomes a ______(negatively/positively) charged ion.

Most atoms become stable when they have 2 electrons in their valence orbital (if the valence orbital is the first orbital), or when they have 8 electrons in their valence orbital (if the valence orbital is the second or third orbital).

Chlorine has a mass number of 25 and an atomic number of 17. It has ______protons, ______neutrons, and ______electrons. There are ______electrons in the first orbital, ______electrons in the second orbital, and ______electrons in the third orbital.

How many valence electrons does it have? ______

Is the atom stable? ______(yes/no)

To become stable, it will have to ______(gain/lose) one electron.

Lets assume the chlorine atom gains one electron to become stable. Because it has gained one electron, it is now a charged atom called an ______.

What is its charge? ______(negative/positive)

Which of the following symbols is correct for a chloride ion?

Cl ______Cl+______Cl- ______

If a chlorine atom gains an electron, then some other atom must lose an electron. An atom with only one valence electron is a good candidate for loosing one electron.

Sodium has a mass number of 23 and an atomic number of 11. It has ______protons, ______neutrons, and ______electrons. There are ______electrons in the first orbital, ______electrons in the second orbital, and ______electron in the third orbital.

How many valence electrons does it have? ______

Is the atom stable? ______(yes/no)

To become stable, it will have to ______(gain/lose) ______electron.

Lets assume the sodium atom looses one electron to become stable. Because it has lost one electron, it is now a ______(positively/negatively) charged ______.

Which of the following symbols is correct for a chloride ion?

Na ______Na+______Na- ______

The sodium ion and the chloride ionhave opposite charges. They are mutually attracted and are held together by the attraction of their opposite charges. This attraction is called an ______bond.

When these ions bond, the result is a ______(molecule/compound) called sodium chloride or simply table salt (NaCl).

When NaCl is put in water, the ionic bond holding the ions together is weakened, and the ions may separate (i.e. dissociate). The result is a solution containing sodium ions (Na+) and ______ions (______).

In general, atoms with 1, 2 or 3 valence electrons tend to loseelectrons and become positively charged ions. Atoms with 6 or 7 valence electrons tend to gain electrons to become stable, and form negatively charged ions.

Positively charged ions are specifically termed ______.

Negatively charged ions are called ______.

  1. Covalent Bonds

Atoms with 4 or 5 valence electrons usually don’t lose or gain electrons, so they usually don't form ions. Instead, they tend to share electrons with other atoms as a way to become stable. When atoms share electrons, they form covalent bonds.

Exception: Sometimes atoms with fewer than 4 electrons or more than 5 electrons in their valence orbitals may also share electrons.

Carbon atoms (atomic number 6) have 4 valence electrons. Carbon atoms need ______more electrons to become stable. It tends to get these electrons by sharing.

How many valence electrons does a hydrogen atom have? ______

With how many hydrogen atoms can a carbon atom share electrons to become stable? ______

When one carbon atom and four hydrogen atoms share valence electrons, there are 8 electrons around the carbon atom and two electrons around each hydrogen atom.

When 2 hydrogen atoms interact, they share electrons. Each hydrogen atom then has ______electrons around it.

The shared electrons join the atoms together. This type of bond is called a covalent bond.

  1. Polar and Nonpolar Covalent Bonds

In a covalent bond, the electrons may be shared equally or may not be shared equally between the atoms. The negatively charged electrons are attracted to the positively charged protons in the nuclei of both atoms. If one atom has more protons than the other atom then it has a stronger positive charge in its nucleus. Any atom with a stronger positive charge in its nucleus will more strongly attract the shared electrons. When this happens, the electrons spend more time around the atom with the stronger attraction (i.e. stronger electronegativity). This means the distribution of charges may become uneven in the compound. This slight imbalance is called polarity.

A molecule with an unequal distribution of charge as a result of unequal sharing is called a polar molecule.

A molecule in which electrons are shared equally between atoms, or in which the distribution of charge around the molecule is uniform, is called a nonpolar molecule.

Note: Molecules are formed by covalent bonds; compounds are formed by ionic bonds, and always contain atoms of different elements.

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