1. Introduction To Chemistry

2. 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.

3. 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

4. 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!

5. 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 Mass 10-20.2 = 10.2 neutrons

6. 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.

7. 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!

8. 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.

9. 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.

10. 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.  12 C = carbon with 6 protons and 6 neutrons  13 C = carbon with 6 protons and 7 neutrons  14 C = carbon with 6 protons and 8 neutrons

11. 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. 13 C and 14 C 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 14 C will have turned into 13 N (nitrogen) atoms.  Researchers use radioactive decay to estimate the ages of rocks and biological remains.

12. 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 14 C) and tracked the radioisotope through steps by which plants produce simple sugars and starches.

13. 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.

14. 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.

15. 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.

16. 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—H 2 O 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.

17. 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.

18. 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

19. 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.