Chemistry

DI BiologyJennifer 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