The Building Blocks of Matter: Atoms - - - + + + + - - + + - - -

Atoms Atoms are the smallest part of an element that has all the Characteristics of the element. If you break an atom apart into sub-atomic particles, they no longer have the properties of the element.

Atoms Smallest possible unit into which matter can be divided, while still maintaining its properties. Made up of: protons neutrons electrons The solar system is commonly used as an analogy to describe the structure of an atom - + For example, what is the smallest possible unit into which a long essay can be divided and still have some meaning? - + + - + + - -

Two major parts of an atom Nucleus (not to scale) Electron Cloud

+ The Atom’s “Center” - - - Protons and neutrons are grouped together to form the “center” or nucleus of an atom. Notice that the electrons are not apart of the nucleus + - - -

Most space between nucleus and electron cloud is empty space.

Nucleus: Center 1. Protons and Where are they located? Nucleus: Center 1. Protons and 2. Neutrons

Review: Subatomic Particles N°  e-

PROTON (p+) positive charge a single, relatively large particle (mass) with a that is found in the nucleus

p+ THE PROTON Fat (heavy, large mass) Positive  (charge) Doesn’t move (lazy) stays in nucleus

Every atom of an element has the same number of protons Every atom of an element has the same number of protons. Carbon atoms always have 6 protons Hydrogen atoms always have 1 proton Uranium atoms always have 92 protons. How many protons does Helium have? __________

NEUTRON (N°) a single, relatively large particle with a neutral charge that is found in the nucleus

THE NEUTRON N°  Fat (heavy) Neutral  (charge) Doesn’t move (lazy)

Number of neutrons in an element can change Number of neutrons in an element can change. It is just like gaining or losing weight. It doesn’t change what the element is- just how much it weighs.(Mass number)

ELECTRON (e-) a single, very small (Mass) particle with a negative charge that is found in a “cloud” around the nucleus

e- THE ELECTRON Skinny (very light) Negative  (charge) Moves a lot (runs around)

Oxygen (O) Atom Notice the two electrons in the first orbital/level and the six in the second + - = 8 How many more electrons can fit in the 2nd orbital/ level? - - - + + + + - - + + - - -

Electron Orbitals… Electrons are what determines how an atom chemically reacts. Electron Cloud:- areas within atoms where there is a high probability of finding electrons.

Energy Levels 3rd shell- 8 electrons 1st energy is closet to the nucleus- it can only ever hold 2 electrons. 2nd shell- 8 electrons 3rd shell- 8 electrons Electrons will always fill shells closet to the nucleus first.

Sodium (Na) Atom Notice the two electrons in the first orbital/level, eight in the second, and one in the third + - = 11 = 12 - - - How many more electrons can fit in the 3rd orbital/ level? - + + + + - - - + + - - - -

Because of this unknown we call the orbitals an “electron cloud” Science has determined where the orbitals are inside an atom, but it is not know precisely where the electrons are inside the orbitals. Because of this unknown we call the orbitals an “electron cloud” Knowing how electrons are arranged in an atom is important because that controls how atoms react with each other to form compounds.

Three Major Sub-Atomic Particles Protons Neutrons Electrons

ATOMIC MASS # (A) The total mass of all of the subatomic particles in an atom (but really # of protons and neutrons)

ATOMIC NUMBER (Z) the number of protons in an atom (assuming the atom is neutral, # of p+ = # of e-)

Example: Sodium Na Atomic Mass # = p+ & N° 22.99 11 Atomic # = # of protons

Another Notation Atomic Mass # = p+ & N° Atomic # = # of protons

To calculate the number of neutrons, subtract the atomic number (smaller) from the atomic mass number (larger) A – Z = # of neutrons

Ex: How many neutrons does Sodium have? Mass # - Atomic # = #N° (You may need to round the atomic #) 22.99 23 - 11 = 12 N° Na 11

ELEMENTS Elements are electrically neutral. (They have the same # of p+ and # of e-)

ION Atoms of the same element that differ in charge. (They have the same # of p+, but different # of e-)

Ex: How many electrons does Sodium have? The atomic number equals the number of protons and the number of electrons. 22.99 11 electrons Na 11

Positive Ions (cations) Negative Ions (anions) Na+ (lost 1 e-) Ca2+ (lost 2 e-) Al3+ (lost 3 e-) Pb4+ (lost 4 e-) H+ (lost 1 e-) Cl- (gain 1 e-) O2- (gain 2 e-) P3- (gain 3 e-) S2- (gain 2 e-) OH- (gain 1 e-)

If an atom GAINS electrons, its overall charge becomes more negative If an atom GAINS electrons, its overall charge becomes more negative. If it LOSES electrons, its charge becomes more positive

ISOTOPE Atoms of the same element that differ in mass. (They have the same # of p+, but different # of N°)

Isotopes are CHEMICALLY the SAME as atoms, but DIFFER PHYSICALLY because they have different masses.

A few examples of isotopes…

So, why do the elements on the PT have masses with decimals???

The average mass of all of the isotopes of a substance AVERAGE ATOMIC MASS The average mass of all of the isotopes of a substance

Example using exam scores!

Example using exam scores! Exam Scores can be weighted higher than homework or quiz grades: What if… Exam 50% Quizzes 20% Homework 30% And you received: Exam 90 Quizzes 80 Homework 70 Your grade = (90 x .5) + (80 x .2) + (70 x .3) = 82

To calculate the average atomic mass: Mass each isotope and multiply by # present Add these products Divide this sum by the total # present

Famous Scientists in Atomic Theory

Democritus (400 B.C.) World is made of 2 things: empty space “atoms”

democritous

(Law of Conservation of Mass) LAVOISIER Found out that the mass of the products must equal the mass of the reactants (in a closed system) (Law of Conservation of Mass)

PROUST LAW OF DEFINITE PROPORTIONS Specific substances always contain elements in the same ratio BY MASS

DALTON LAW OF MULTIPLE PROPORTIONS The ratio of masses of 1 element that combine with a constant mass of another element can be expressed in whole numbers