Chapter 4.3 The Atom

The Atom The smallest particle of an element that retains its identity in a chemical reaction

Three Kinds of Subatomic Particles Electrons Negatively charged Surround the nucleus Protons Positively charged In the nucleus Neutrons Neutrally charged

Three Kinds of Subatomic Particles Remember: the mass of one proton is about the same as the mass of one hydrogen atom!

Structure of the Atom Atoms are made up mostly of empty space At the center of the atom is the nucleus Central core made up of protons and neutrons Contribute most of the mass of an atom Positively charged

Structure of the Atom Surrounding the nucleus are orbitals of negatively charged electrons Today, known as the electron cloud

What makes one atom different from another? The number of protons! A difference in number of protons changes the actual element You can change the number of electrons and neutrons and still have the same type of element

Reading the Periodic Table

How do we know how many subatomic particles are in each element? Protons – Look at the atomic number! Electrons – Atoms are neutrally charged, so the number of protons = number of electrons

How do we know how many subatomic particles are in each element? Neutrons – The mass of the atom is made up of protons and neutrons # neutrons = mass number – atomic number Mass number is not the same as atomic mass, it is rounded to a whole number!

Shorthand Notation

Bohrs Atomic Model 1915 Protons and Neutrons are in the nucleus Electrons are outside the nucleus in specific orbitals Electrons can move from one orbital to another, and release energy as electromagnetic radiation.

Drawing Bohr’s Models Atomic model that shows the electrons surrounding the nucleus in orbitals How many electrons can fit in each orbital?

Drawing Bohr’s Models n = principal quantum number The number of the energy level or orbital

Drawing Bohr’s Models Use the principal quantum number to calculate the number of electrons in each orbital

Lewis dot structures Valence electrons – electrons in the highest occupied energylevel/orbital of an atom Maximum of 8 valence electrons Use the periodic table to determine!

Why are valence electrons so important? Tells us the chemical properties of an element They are responsible for the formation and breaking of bonds

Lewis dot structures We use Lewis dot structures to show the number of valence electrons within an element

Do Now! Find Neon on your periodic table. What is the atomic number and mass number? How many protons, neutrons, and electrons does Neon have? What is the shorthand notation and hyphenated notation for Neon?

Do Now! What is an isotope? How does one isotope differ from another?

Calculating Atomic Mass

Isotopes Many elements have at least two or more naturally occurring isotopes Some isotopes are found more than others We call this it’s percentage abundance

Average Atomic Mass The atomic masses found on the periodic table is the weighted average of the isotopes of an element An isotope with a larger percent abundance will contribute more to the weighted average than an isotope with a smaller percent abundance

Convert percentages into decimals What if you had two isotopes of an element: one with a mass of 15 amu and 25% abundance and another with a mass of 10 amu and 75% abundance? Convert percentages into decimals Divide by 100 Multiply the mass of each isotope by its percent abundance in decimal form Add the numbers together Ex: 25% → 0.25 75% → 0.75 (15 amu x 0.25) = 3.75 (10 amu x .75) = 7.5 3.75 + 7.5 = 11.25 amu

Practice! There are 3 naturally occurring isotopes of hydrogen Hydrogen – 1 has a mass of 1.0078 amu and has a percent abundance of 99.985 % Hydrogen – 2 has a mass of 2.0141 amu and has a percent abundance of 0.015% Hydrogen – 3 has a mass of 3.0160 amu and is so rarely found in nature it’s percent abundance is considered negligible

Practice! Chlorine has two naturally occurring isotopes Chlorine – 35 has a mass of 34.969 amu and it’s percent abundance is 75.77% Chlorine – 37 has a mass of 36.966 amu and it’s percent abundance is 24.23%

Some tips Check your periodic table to see if you are correct! Write out ALL your work! Do not round anything until the problem is finished! Round your final answer to TWO decimal places