Introduction to Molecules

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Why Chemistry? To understand the chemical reactions that occur in the human body, it is essential to have some knowledge of basic chemistry. So let’s learn a bit of chemistry!

Elements All matter is made of elements. There are 117 known elements, of which 92 occur in nature. The other 25 are produced in laboratories and exist for very short periods of time. You can view the periodic table of elements at

Matter Matter has both volume and mass. When matter consists of a single element, for example oxygen (O 2 ), all the matter is virtually identical. That means O 2 is O 2. Matter can take the form of a liquid, a solid, or a gas. Yes, gases are matter. When a balloon is inflated with helium, the volume of helium makes the balloon expand and the mass is increased.

Is energy a form of matter? Choose a button below: YESNO

Sorry! Energy is not matter! Energy has no mass or volume. Energy cannot be weighed and it does not take up space. All elements have mass and volume, so all matter formed from elements has mass and volume.

Good! Energy is not matter because it does not have mass and volume. Some Common Elements Carbon (C) Calcium (Ca) Potassium (K) Nitrogen (N) (Colorless) Copper (Cu) Pictures from:

Elements in the Human Body Major Elements—the body contains large quantities of these elements. Minor Elements—the body contains lesser amounts of these elements Trace Elements—the body contains very small amounts of these elements

Elements in the Human Body Four major elements make up 96% of the mass of a human body. The four major elements in descending order of their relative mass in the body are: Oxygen, Carbon, Hydrogen, and Nitrogen.

Elements in the Human Body Copy this chart in your notebook. MajorMinorTrace OxygenCalciumAluminum CarbonChlorineCopper HydrogenIronIodine NitrogenPhosphorousZinc Potassium Sodium Sulfur

Symbols of Elements Chemical symbols are often the first letter of the element’s name in upper case form. For example, the symbol for carbon is C. Because several elements begin with the same first letter, for some elements the first and second letters of the name are used. The second letter is in lower case. For example, the symbol for chlorine is Cl. Sometimes the Latin version of the element’s name is used. For example, the symbol for iron is Fe from the Latin word Ferrum.

Symbols of Elements Write the correct symbol next to the name of each of the elements in the human body you copied into your notebook. If you are not sure of a symbol, make a guess based on what you’ve learned about how symbols are determined. Be careful of upper and lower case letters! After you have listed the symbols, go to the next slide.

Chemical Symbols Check your answers MajorMinorTrace Oxygen OCalcium CaAluminum Al Carbon CChlorine ClCopper Cu Hydrogen HIron FeIodine I Nitrogen NPhosphorous PZinc Zn Potassium K Sodium Na Sulfur S Make corrections in your notes.

How are chemical symbols made? Choose the best answer below: A. The first letter of each element’s name. B. The first and second letter of an element’s name, both upper case. C. The first letter or the first and second letters of the element’s name. The first letter is upper case and the second letter is lower case.

SORRY! Go Back and Try Again Chemical symbols are often the first letter of the element’s name in upper case form. Because more than one element begins with the same letter, this system can not be used for all elements. Sometimes the first and second letter are used. The second letter is lower case, for example Cl. For a few elements, the Latin version of the element’s name is used; for example Fe is from the Latin word Ferrum for iron.

Very Good! You are ready to move on to the next topic.

Atomic Structure Elements are made of atoms. An atom is the smallest whole particle of an element. Atoms have 3 major sub-particles and some of these sub-particles have charges: –Protons—positive charge –Electrons—negative charge –Neutrons—no charge

Atomic Numbers The number of protons in an atom determines the atom’s atomic number. The atomic number of an atom is equal to the number of protons in the atom. For example, an element with the atomic number 2 has 2 protons, each with a positive charge. So there is a total of 2 positive charges.

Atomic Charges The number of protons in an atom is equal to the number of electrons. Consequently, the number of positive charges equals the number of negative charges, resulting in a net charge of zero. Therefore, atoms do not have a charge and are considered to be neutral.

Choose One Oxygen has 8 protons and 8 electrons. Oxygen has 16 protons and 8 electrons. Oxygen has 8 protons and 16 electrons. Let’s practice using atomic numbers to determine atomic structure: Oxygen has the atomic number 8. Therefore,

Sorry! Go Back and Review Once More:

Good Job! Now Let’s Look At Atomic Structure Protons and Neutrons are located in the nucleus. Electrons are moving in orbits outside the nucleus. The outer most electrons are called valence electrons. Oxygen has 6 valence electrons and Carbon has 4 valence electrons. C O Valence electrons Nucleus with 8 protons and 8 neutrons Valence electrons Nucleus with 6 protons and 6 neutrons

Reminder: Carbon has an atomic number of 6. How many electrons does it have? Choose One: 6 electrons 12 electrons

Yes! The atomic number tells you both the number of protons and the number of electrons. Carbon has the atomic number 6. Therefore, it has 6 protons and 6 electrons. Note, the atomic number does not indicate the number of neutrons.

Check Your Understanding Nitrogen has an atomic number of 7. Using only the information given above, determine and write in your notebook the number of each of the following components in a nitrogen atom: –protons –electrons –neutrons –positive and negative charges

Check Your Understanding The nitrogen atom has: –7 protons and 7 electrons, –7 positive and 7 negative charges, –the number of neutrons can not be calculated using only the atomic number. Click here if you want to review more: Click here if you are ready to proceed:

Valence Electrons Valence electrons are very important in chemical reactions. Valence electrons can be transferred from one atom to the valence shell of another atom, or the valence electrons from two atoms can be shared.

Valence Electrons When valence electrons are transferred from one atom to the valence shell of another atom, the atoms involved either gain or lose electrons. When an atom gains or loses electrons it becomes an ion. An ion is an atom with an electrical charge. Atoms that gain electrons become negatively charged ions. Atoms that lose electrons become positively charged ions.

Ions Examples: Cl + 1e- Cl - Na – 1e- Na + Ions in your body are called electrolytes, and are very important for carrying electric currents or impulses between cells.

Valence Electrons When the valence electrons of two atoms are shared, the atoms remain neutral. An atom can share each of its valence electrons. Example: Methane CH 4 C H HH H Red=electron from H Black=electron from C

Chemical Bonds Two or more atoms can join together to form a new unit. The force holding the atoms together is called a chemical bond. When valence electrons are transferred or shift in location an ionic bond forms between the atoms. The bond is formed due to the attraction of opposite charges. When valence electrons are shared between atoms a covalent bond forms between the atoms. The bond is formed due to the physical sharing of the electrons.

Chemical Bonds Chemical bonds form due to the force of attraction between the atoms. The stronger the force of attraction, the stronger the bond. Chemical bonds are analogous to glue. Bonds vary in strength from very weak to very strong, just as different glues have varying holding strengths—consider a glue stick compared to super glue.

Types of Bonds Ionic Bonding = transfer of electrons Covalent Bonding = sharing of electrons Breaking bonds requires energy! AND Breaking bonds releases energy!

Ionic Bonding When atoms transfer electrons, they become ions and have either positive (+) or negative (-) charges. Example: Na - 1e - Na+ 1 (ion) ( Sodium losing 1 electron) (Sodium ion with +1 charge) Cl + 1e- Cl -1 (ion) (Chlorine gaining an electron) (Chlorine ion with -1 charge)

Ionic Bonding Opposite charges attract and ionic bonds can be formed creating a compound known as a salt. Example: Na + + Cl - NaCl (sodium chloride) Ions Table Salt

Covalent bonds Electrons are shared between atoms. Hydrogen Molecule or H 2 H H H H

Molecules Molecules are formed when two or more atoms are joined together by covalent bonds. These atoms can come from the same or different elements. Examples: O + O O 2 C + H + H + H + H CH 4 atom + atom molecule

Compounds Compounds are a type of molecule. Compounds are formed when two or more different elements chemically react and form bonds to produce a new substance which has different properties than the elements had alone. Example: 2H 2 + O 2 2 H 2 O

Compounds Compounds have very different properties from the elements in their pure form. Na = sodiumCl = chlorine –a very dangerous metal- a very dangerous gas –not found in pure form on this planet - rarely found in nature on this planet NaCl = sodium chloride which is table salt

Chemical Reactions Chemical reactions occur when: –Atoms, molecules, or ions interact Existing chemical bonds are broken New chemical bonds are formed Breaking bonds requires energy! AND Breaking bonds releases energy!

Chemical Equations Chemical equations are “chemical sentences” showing what is happening in a reaction. Example: X + Y XY (reactants) ( reacts to form) (product) What does the equation below mean? 2H 2 + O 2 2H 2 O

Answer: 2 H 2 + O 2 2 H 2 O 2 Hydrogen molecules plus 1 Oxygen molecule react to form 2 molecules of water. The hydrogen and oxygen molecules are the reactants and the water molecules are the products. Were you correct? If yes, proceed. If not, go back and review or ask for clarification from your teacher.

Nice Work! You now have a basic knowledge of chemistry that you will use in your continued study of the biomedical sciences. Microsoft clip art