Chemistry Review

1. Chemistry Review

2. ELEMENTS OF LIVING MATTER • OXYGEN • CARBON • HYDROGEN • NITROGEN

3. There are other elements that are important also… • Potassium • Sulfur • Calcium • Phosphorus • Iron • Sodium IN ANIMALS: IN PLANTS: Helps maintain the fluid & electrolytes in the body. In some amino acids Component of bones & co-factor in some enzymes co-factor in some enzymes Phosphate groups in ATP In hemoglobin (haemoglobin) & in cytochromes in cytochromes In membrane functions & sending nerve impulses

4. HELIUM ATOM NUCLEUS ELECTRONS NEUTRONS ORBITAL Proton # changed= new element Electron # changed= a charged ion Neutron # changed= an isotope PROTONS

5. Some discussion questions • How many electrons fit in each orbital? • How does the proton number compare to the electron number? • What is the trend of electronegativity among atoms? • How do you think the number of electrons on the outer orbital of each atom relates to how stable the element is? • Which elements are the most reactive? 2 on the s orbital and 8 on the next two p orbitals They’re the same on an element if it is unaltered/uncharged Increases from left to right across a row and decreases from top to bottom down a column Atoms with full outer shells are more stable & less reactive; elements made of atoms with partially complete outer shells are more reactive; the closer the atom is to having a completely full or completely empty outer shell the more violently it reacts with other atoms. The halogens; column VII

6. Isotopes • Is an atom with more neutrons than “normal” • = greater mass • Isotopes can be stable such as C-13 or they can be unstable like C-14. • C-14 is a radioactive isotope • Its nucleus decays spontaneously, giving off particles of energy. • When the decay goes on long enough it will change the number of protons which will then change to a different element. • EX: C-14 will change to N. • What are some uses? • Fossil dating • Used as tracers • Provide high quality imaging of organs & detecting tumors… • Allow produce to have a longer shelf-life.

7. Ionic Bonding • A strong bond • Opposite charge atoms bond & an electron is lost by one atom & gained by the other. • Cation: when the charge of an atom is positive • The atom lost an electron • Anion: when the charge of the atom is negative • The atom gained an electron

8. NaCl Crystal The formation of the ionic bond in table salt Ionic Bonds Everyday tablesalt

9. Which atoms are the anions & which are the cations? LiCl anion cation MgO

10. Discussion Questions The atoms in column VII because they are only missing one electron & they have the high electronegativity needed to steal one from another atom • Which elements of the periodic table tend to become negative ions (greatest potential for gaining an electron)? Why? • Which ones tend to become more positive (have the weakest ability to keep their electrons)? Why? • Which columns would combine well in order for both to be more stable? • Which elements on the periodic table tend to make ionic bonds? • How does electronegativity correlate with ionic bonding? • Why don’t all the elements of the periodic table form ionic bonds? • What do atoms that cannot form ionic bonds do to become more stable? The elements to the far left in column I, because they have low electronegativity & have only 1 electron on their outer orbital Columns I and VII, columns II and VI Columns I and VII, columns II and VI Atoms with high electronegativity are able to steal electrons most easily, atoms with low electronegativity tend to have their electrons stolen from them At some point an element is unable to steal enough or give enough electrons in order to become stable because it does not have enough electronegativity to steal as many electrons as it needs or it has too much electronegativity to give away as many as would be necessary. Form a covalent bond

11. Covalent Bonding VERY STRONG BOND HOW DOES THIS HAPPEN? WHY DOES THIS HAPPEN?

12. Attraction of electrons to the protons

13. The number of open places on the valence shell determines the number of bonds it can make. How do the valence electrons influence molecular bonding? A large difference between electronegativities of 2 atoms then the one w/higher electronegativity can steal electrons from the other. If both are fairly equal then they will form a covalent bond. How does electronegativity influence molecular bonding?

14. HOW MANY BONDS CAN THE FOLLWING ATOMS MAKE? • HYDROGEN • OXYGEN • CARBON 1 2 4

15. POLAR vs NONPOLAR Polar= when one atom is bonded to another and the electronegativity is not the same causing the electron(s) of one atom to be shared unequally or the asymmetrical arrangement of the molecules Nonpolar= when there is an equal sharing of electrons between two different atoms or because of the symmetrical arrangement of polar bonds.

16. HYDROGEN BONDING: DRAW 2-3 MOLECULES OF WATER & INDICATE THE HYDROGEN BONDS Not effective over long distances WEAK BONDS Formed by the attraction of opposite partial electric charges between two polar molecules

17. Draw a hydrogen atom & fluorine atom (no need to worry about the neutrons & protons this time) WHICH ATOM WOULD BE CONSIDERED MORE ELECTRONEGATIVE? WHY? HOW CAN THESE ATOMS BECOME MORE STABLE? WHAT DO YOU CALL THIS?