Atom Lab
The smallest units of all matter, including living matter, are known as atoms. There are 92 different kinds of natural atoms found in nature and several others that have been manufactured by smashing other atoms together. These quickly disintegrate. A kind of matter that consists exclusively of one kind of atom is known as an element. Atoms can be combined in many ways to form millions of different kinds of molecules. Each kind of molecule has a specific arrangement of atoms within its structure. Kinds of matter that are composed of only one kind of molecule are called compounds.
Each kind of atom has a specific number and arrangement of parts that differs from the number and arrangement of parts in other kinds of atoms. The specific structure of an atom determines the kinds of atoms that it can bond with to form larger molecules. Each atom consists of protons, neutrons, and electrons arranged with the positively charged protons and uncharged neutrons located in a central area called the nucleus and with the negatively charged electrons moving around outside the nucleus in specific regions known as orbitals.
Figure 2.1 is a periodic table of the elements that arranges elements in order of increasing complexity and according to the way they react chemically. Do not attempt to memorize it. (There probably isn't much chance of that any-way.) This table contains a lot of information. Most important, the periodic table identifies the number of protons, neu-trons, and electrons in atoms of each element. Figure 2.2 interprets some of the information about a carbon atom from the periodic table. The symbol for carbon is C. The number at the top is the atomic number, which tells you how many protons or electrons are in the atom. The number at the bottom, the mass number, is the sum of the number of protons and neutrons in the atom. You can determine the number of neutrons in this atom by subtracting the atomic number 6 from the mass number 12 (rounded off); you will find that there are 6 neutrons in a carbon atom (12 - 6 = 6), To determine the number of protons, electrons, or neutrons in an atom, use the periodic table and the following equations;
1. Atomic number = number of protons
2. Atomic number = number of electrons (in a neutrally charged atom)
3. Mass number (rounded off) - atomic number = number of neutrons (in a typical atom)
Atoms have the same number of positively charged (+) protons and negatively charged (-) electrons therefore, the atom has no net charge. Beçause opposite charges are attracted to one another, the moving electrons are held near the nucleus but their movement prevents them from being pulled into the nucleus. Because the electrons repel each other and are light and move very rapidly, there is a tendency for electrons to move around the nucleus in specific regions called orbitals. The distance of electrons and their orbitals from the nucleus is determined by the amount of energy the electrons possess. Electrons with the greatest energy are found in the orbitals farthest from the nucleus. Energy levels (Ist, 2d, 3d, etc.) designate differences in an electron's energy and distance from the nucleus. Two types of orbitals occur in atoms of the first 20 elements: s (spherical) orbitals and p (propeller) orbitals. All orbitals are full when they have two electrons. The first energy level contains just a single s orbital (Is) that may hold a maximum of two electrons. The second and third energy levels each contain an s orbital (2s and 3s) and three additional p orbitals designated px, py, and pz (2px, 2py, 2pz and 3px, 3py, 3pz). Each of these orbitals also may hold only two electrons but because there are 4 orbitals in the second energy level (2s, 2px, 2py, 2pz) the second energy level can hold up to 8 electrons. The general rules concerning electron distribution are:
1. Electrons always fill lower energy levels first.
2. The s orbital of any given energy level is filled before electrons occupy p orbitals.
3. One electron occupies each p orbital of a given energy level before a second electron is added to any p orbital.
Therefore, an atom of the element fluorine that has a total of nine electrons has two electrons located in the Is orbital, two located in the 2s orbital, two in the 2px orbital, two in the 2py orbital, and one in the 2pz orbital.
Molecular Structure
Specific atoms may be combined in certain ways to form larger units called molecules. The bonding together of atoms is a very precise process. Some kinds of atoms are very reactive and will combine with one or two other kinds of atoms.
We will not try to determine why certain atoms combine into molecules but rather how this process happens.
lonic Bond
Some kinds of atoms have such a strong attraction for electrons that they steal electrons from other atoms that have rather loosely held electrons. The specific structure of an atom determines whether it will form an ion. Ions are atoms or molecules that have gained or lost electrons and, therefore, are either negatively or positively charged. Atoms that lose electrons are positively charged (+), and atoms that gain electrons are negatively charged (-). Those ions that have the same charge (both + or both -) repel one another, whereas those with unlike charges attract one another and form an ionic bond.
1. Figure 2.7 contains models of different ions. Cut them apart and assemble them to form as many different kinds of compounds (combinations of ions) as you can.
2. List at least five compounds in the following space. (Chemists generally write the formula of ionic compounds by writing the symbol for the positive ion first and then the negative ion. They use a subscript to indicate the number of ions needed to balance the charge. For example the formula MgCl, means that there is a single magnesium ion (Mg**) bonded to 2 chloride ions (CI-) to make the salt magnesium chloride.
Covalent Bonds
A second kind of bond that holds atoms together to form molecules is known as a covalent bond. In covalent bonds, the electrons are not actually transferred from one atom to another as in the formation of ions and ionic bonds, but are shared by two or more atoms. Each pair of electrons that is shared is the equivalent of one covalent bond. Chemists typically diagram molecules by using a line between atoms to represent a single covalent bond.
Figure 2.6 indicates that a single carbon atom (C) is sharing four electrons with four different hydrogen atoms
(H) and that each of the four hydrogen atoms is sharing an electron with the same carbon atom. If you know how many electrons each atom is able to share, you should be able to diagram a variety of different kinds of atoms. Sometimes two atoms may share more than one pair of electrons, creating a double bond, for example, the carbon dioxide molecule
has the following structure; 0 = C = 0. The diagram of the carbon dioxide molecule indicates that a carbon atom is
sharing two electrons with one oxygen atom and two electrons with another oxygen atom. Each oxygen atom shares two electrons with the same carbon atom.
Making Diagram Arrangement
1. Begin with the carbon atoms and bond them together in a chain or a ring.
2. Next, add the nitrogens if any are called for.
3. Then add the oxygens, if any.
4. Finally, count the number of electrons in the whole molecule that are still available for bonding. (If this number is equal to the number of hydrogen atoms called for, simply add one hydrogen to each bondable point.) If there are too few hydrogens to complete available bonds, find two free bondable electrons on adjacent atoms and have them form a second bond between themselves (double bend). Now count the available bonding points— the number of hydrogens called for should equal the number of bondable electrons-—and simply add the hydrogens where they can share electrons.
Acids, Bases, and pH
Acids are molecules that release hydrogen ions (H*) when dissolved in water. A hydrogen ion is a hydrogen atom that has lost its electron. Substances that remove hydrogen ions from solution are known as bases. It is frequently important to know if a solution is an acid or a base, and a number of different methods have been developed to test solutions for their acidity or alkalinity. All of these systems rely on a scale known as the pH scale, which is a measure of the number of hydrogen ions present in a solution. Pure water has both hydrogen ions (H*) and hydroxide ions (OH-) present in equal numbers, because water molecules dissociate (HOH→ H+ + OH-). Solutions with equal numbers of hydroxide and hydrogen ions are called neutral solutions. If there are more H+ than OH, then the solution is an acid. If there are more OH- than Ht, then it is a base (alkaline). The pH scale shown in figure 2.8 indicates the range of acidity and alkalinity that can exist. There are a couple of important things that you should know about the pH scale. First, it is a logarithmic scale, which means that the difference between any two numbers on the scale is a difference of 10 times. Sec-ond, it is an inverse scale, which means that the smaller the pH number the more hydrogen ions (H*) are present.
Therefore a solution which has a pH of 5 is 100 times more acid than a solution with a pH of 7.
ADD LAB DIAGRAM
LAB PT2
A chemical reaction occurs when atoms or molecules react with one another in such a way that chemical bonds are broken and new molecular combinations are made as new bonds are formed. In many cases, there is physical evidence that a reaction has taken place. This evidence might be some visible change such as the production of a gas that bubbles off, a color change, the production of heat, or the development of an insoluble material that settles to the bottom of the con-tainer. As reactions occur between two chemical reactants, the chemical bonds generally rearrange to form a more sta-ble, longer-lasting end product.
Chemical equations are shorthand statements used to represent chemical reactions. The reactants, which are changed are shown on the left and the new substances formed (products) are on the right. The arrow indicates the direction of the chemical transformation. For example, hydrogen reacts with oxygen to form water.
2H2 + 02 -> 2H20 (water)
Reactants
Products
Look carefully at the way the equation is written. Because hydrogen and oxygen exist as molecules consisting of two atoms, rather than as individual H and O atoms, we must write them as such in the equation.
ADD QUESTIONs
Study Guide: Atoms and Molecules
Key Concepts:
Atoms: The smallest units of all matter, including living matter. There are 92 different kinds of natural atoms found in nature and many others manufactured by smashing atoms together, which disintegrate quickly.
Elements: Matter that consists exclusively of one kind of atom.
Molecules: Combinations of atoms arranged in specific structures. There are millions of different kinds of molecules, each with a specific arrangement of atoms.
Compounds: Kinds of matter composed of only one kind of molecule.
Atomic Structure:
Atom Components:
Protons: Positively charged particles in the nucleus.
Neutrons: Uncharged particles also in the nucleus.
Electrons: Negatively charged particles moving around the nucleus in orbitals.
Nucleus: The center of an atom, housing protons and neutrons.
Orbitals: Specific regions outside the nucleus where electrons are likely found. The distance from the nucleus depends on the amount of energy the electrons possess.
Electron Distribution:
Energy Levels: Designated as 1st, 2nd, 3rd, etc., representing the distance of electrons from the nucleus.
Types of Orbitals:
s Orbitals: Spherical-shaped orbitals, holding a maximum of 2 electrons.
p Orbitals: Propeller-shaped orbitals, each can hold 2 electrons (px, py, pz).
Filling Rules for Electrons:
Electrons fill lower energy levels first.
s orbitals of any given energy level fill before electrons occupy p orbitals.
Each p orbital is singly occupied before any pairing occurs.
Types of Bonds:
Ionic Bonds: Formed when one atom with a strong attraction for electrons steals electrons from another atom.
Ions:
Positively charged atoms lose electrons (+).
Negatively charged atoms gain electrons (-).
Opposite charges attract, forming an ionic bond.
Covalent Bonds: Formed by the sharing of electrons between atoms.
Each pair of shared electrons counts as one covalent bond.
Diagrams: Typically use a line between atoms (e.g., carbon (C) shares four electrons with four hydrogen (H) atoms)
Double Bonds: Two pairs of electrons shared (e.g., CO2 structure: O=C=O).
Acids, Bases, and pH:
Acids: Molecules that release hydrogen ions (H+) in solution (which are hydrogen atoms that have lost an electron).
Bases: Substances that remove hydrogen ions from a solution.
pH Scale: A measure of the concentration of hydrogen ions in a solution.
Pure water has equal H+ and OH- ions, resulting in a neutral pH (7).
Solutions with more H+ are acidic (<7), while those with more OH- are basic (>7).
The pH scale is logarithmic; a pH difference of one signifies a tenfold difference in H+ concentration.
Chemical Reactions:
Occur when atoms or molecules react, breaking chemical bonds and forming new combinations as new bonds are made.
Chemical Equations: Shorthand statements representing chemical reactions, where reactants are shown on the left and products on the right (e.g., 2H2 + O2 -> 2H2O).
Important Equations:
Atomic number = number of protons
Atomic number = number of electrons (in a neutrally charged atom)
Mass number (rounded off) - atomic number = number of neutrons (in a typical atom)