Chemistry Review

ELEMENTS OF LIVING MATTER OXYGEN CARBON HYDROGEN NITROGEN OXYGEN CARBON HYDROGEN NITROGEN

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

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

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? Some discussion questions 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

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.

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

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

Which atoms are the anions & which are the cations? LiCl MgO

Discussion Questions 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 atoms in column VII because they are only missing one electron & they have the high electronegativity needed to steal one from another atom 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 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

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

Attraction of electrons to the protons

How do the valence electrons influence molecular bonding? How does electronegativity influence molecular bonding? The number of open places on the valence shell determines the number of bonds it can make. 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 MANY BONDS CAN THE FOLLWING ATOMS MAKE? HYDROGEN OXYGEN CARBON

POLAR vs NONPOLAR Nonpolar= when there is an equal sharing of electrons between two different atoms or because of the symmetrical arrangement of polar bonds. 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

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

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?