# DI Biology Jennifer Naples

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DI Biology Jennifer Naples
Chemistry DI Biology Jennifer Naples

Elements An element is a substance that can not be broken down into smaller substances There are 90 naturally occurring elements in nature All elements are listed in the periodic table

Periodic Table of Elements
The periodic table of elements

Elements There are 25 elements needed for all living things
96% of the mass of human beings is: Carbon Hydrogen Oxygen Nitrogen

Atoms An atom is the smallest part of an element
There are 4 parts in the arrangement of an atom Nucleus - the center of an atom Proton - (+)charged particle found inside of the nucleus Electron-(-)charged particle found outside the nucleus Neutron – Particle found inside the nucleus with NO charge

Energy Levels Regions where electrons travel around the nucleus
Each energy level can hold a certain number of electrons 1st energy level can hold 2 electrons 2nd level can hold 8 electrons 3rd energy level can hold 18 electrons All energy levels must be used in order for an element to be stable

Example If an element has 8 total electrons, two will be in the first energy level and the remaining 6 will be in the second level. Is this element stable? NO! The second shell is not full How many electrons would this element need in the second energy level to be stable? 8

Electron Configuration
Draw the electron configuration for an atom that has 9 electrons. Is it stable? Draw the electron configuration for am atom that has 16 electrons. Is it stable?

Atomic Number The number found above an element on the periodic table
Is equal to the total protons in the nucleus Also indicates the number of electrons since protons and electrons always equal one another

Determining the Number of p+, n and e-
Protons are always equal to the atomic number Carbon’s atomic number is 6=6 protons Electrons are also equal to the atomic number Unless it is an ion(+ or – charge) Neutrons=atomic mass - atomic number Carbon = 12 atomic mass, 6 atomic number = 6 neutrons

Practice Problem Find the number of protons, neutrons and electrons for helium: 2 protons, 2 neutrons, 2 electrons

How Elements Combine Compound – a substance that is made from two or more different elements bound together Example: Salt(NaCl) or water (H2O) Molecule – a group of atoms held together by covalent bonds Example: oxygen (O2)

Ions Sometimes atoms have a charge
The charge can be either positive or negative An ion is created when an atom gains or loses an electron This charge changes the # of subatomic particles in the element Example: Na+2

Ions Figuring out the number of P,E and N in an ion:
First figure out the structure for the atom Change the # of electrons according to the charge listed near the element K+2 K has 19 electrons K+2 has a +2 positive charge Take AWAY 2 electrons K+2 has 17 electrons

Ions Try it yourself: Find the number of electrons for N-1
What is the number of electrons for N? 7 What is the number of electrons for N-1

Compounds and Bonding Compound – a substance composed of elements that are chemically combined What does it mean to be chemically combined Chemical vs. Physical change

Compounds and Bonding Why do elements combine?
Electrons surround the nucleus in energy levels In order to be stable the outer valance shell must be filled The pull on an atom on another electron is known as electronegativity More electronegativity=more pull on electrons

Covalent Bonds When two atoms share electrons Example: water
Strong bonds Most living things are made Up of covalent bonds

Ionic Bonds When two elements of opposite charge combine.
An ion is an atom that has acquired a positive or negative charge Example: Na+Cl = NaCl Weak bonds

Chemical Reactions When they occur: Bonds are formed Bonds are broken
Substances are changed or altered into different substances

Metaboliosm Refers to the chemical reactions that take place within an organism

Chemical Equations Reactants – substances that undergo the reaction
Products – substances which are formed from a reaction Subscripts – The number of atoms of each element in a molecule Coefficient – The number before each chemical formula(number of molecules of that substance)

Examples of Chemical Equations
Water

pH pH – refers to the hydrogen ion (H+) versus hydroxide ion (OH-) concentration in a solution Acid – a substance that has more H+ ions and has a pH BELOW 7 Base – a substance that has more OH- ions and has a pH ABOVE 7

pH Scale

pH Examples Pure water has a pH of 7.0 which means it has a equal amount of H+ and OH- ions Hair remover(Nair) has a pH of 13.0 Soda has a pH of 3.0

Ionization When a nonionic compound is converted into ions
Water can go through this process. Water can be converted into H+(Hydronium ions) and OH-(Hydroxide ions)

Atomic Mass The number found below an element on the periodic table.
Is equal to the total protons and neutrons in a nucleus