The Structure of Atoms Section 4.2

You want to be able to … describe the general structure of the atom, and explain how the properties of the first 20 elements in the Periodic Table are related to their atomic structures Something to keep in mind …

Atom – the smallest particle of an element that retains the properties of that element. When we say “small,” we mean “SMALL!” A typical copper penny contains 29,000, ,000,000,000,000 atoms Current world population is about 7, 382,000,000 people Defining the Atom

There are two main parts in each atom Nucleus – Protons – Neutrons Electron Cloud – Electrons – Lots and lots of empty space Parts of the Atom

Protons are located in the nucleus These are positively charged subatomic particles. Carries a single unit of positive charge (+1) Mass is one AMU, which is 1/12 of the mass of an atom of Carbon-12 Protons

Neutrons are located in the nucleus These are subatomic particles with no charge Their mass is about the same as that of the proton, one AMU. Neutrons

Electrons are located in the electron cloud. Carries a single unit of negative charge (-1) The mass of an electron is about 1/1840 th that of a proton or neutron Electrons

ParticleSymbolRelative Charge AMU Proton p+p+ +11 Neutron n0n0 01 Electron e-e- 1/1840 th Comparison of Particle Properties

There are differences among the number of subatomic particles. How can we tell atoms of different elements apart?

Quick Practice! Use your Periodic Table to complete the “Elements and Their Symbols” worksheet. First – we need to become familiar with the Periodic Table

The atomic number of an element is the number of protons in the nucleus of the atom of that element. Where can I find this? Look on the Periodic Table Atomic Number

Elements are arranged in the Periodic Table according to their atomic number

Locate any element on the Periodic Table The atomic number = the number of protons in every atom of that element Atomic Number Every atom of Cobalt contains 27 protons

How do you know the number of electrons in an atom? Since atoms are neutral, the number of electrons in an atom must equal the number of protons. It takes one electron to cancel out the charge from one proton. Electrons

– This tells you the mass (in grams) of one mole of atoms of an element. – A mole is a counting unit for atoms, similar to a dozen, but MUCH larger – Atomic mass can be used to determine the number of neutrons in an “average” atom – This number is found on the Periodic Table Atomic Mass This is the Atomic Mass of Cobalt

Periodic Table Practice Sheet – Use the periodic table to obtain information about the number of protons and electrons for a given element. Quick Practice!

The total number of protons and neutrons in the nucleus is the mass number of the atom. Mass number is NOT found on the Periodic Table Number of Protons + Number of Neutrons = Mass Number The units for mass number are “AMU” which stands for atomic mass unit. Mass Number

What is the mass number of an atom that has 8 protons and 8 neutrons? And, what is the identity of this element? How do you find the mass number? 8 protons + 8 neutrons = 16 AMU How do you identify the element? 8 protons means that the atomic number is 8, which means this is oxygen. Calculating Mass Number

Determine the number of neutrons in an atom of Boron that has a mass number of 11? How do you determine the number of neutrons? Mass number – Atomic Number = Number of Neutrons 11 (Mass number) – 5 (Atomic Number) = 6 Neutrons Using Mass Number to determine neutrons

How many protons, neutrons and electrons are there in one atom of Helium-4? Number of Protons = atomic number 2 protons Number of Electrons = Number of Protons 2 electrons Number of Neutrons = Mass number – Number of Protons 4 – 2 = 2 Neutrons Try this example …

How can you find the number of neutrons in an “average” atom of an element? Look at the atomic mass on the Periodic Table. Round the atomic mass to the nearest whole number. Use this as your mass number. Using mass number – atomic number, solve for the number of neutrons in an “average” atom. Number of Neutrons, Continued

Isotopes are atoms of the SAME element with different numbers of neutrons. Therefore, isotopes for the same element will have the SAME ATOMIC NUMBER but have DIFFERENT MASS NUMBERS Isotopes

There are two ways to write the symbol for an isotope. #1 is Nuclear Symbol Isotopes are written as the chemical symbol with two additional numbers to the left side of it B Mass number is a superscript Atomic number is a subscript. Expressing Isotopes

#2 = Hyphen notation, which is a shorthand for the nuclear symbol. Lithium–7 Li-7 The name of the element or symbol is written first There is a dash and then the mass number is written Expressing Isotopes

What is the atomic number? 18 What is the atomic mass? amu How many protons, neutrons and electrons are in an atom of Rubidium if the mass number is 40? 18 protons, 18 electrons 22 neutrons Putting it all together 40 (mass number)- 18 (atomic number) = 22 neutrons

Atomic Number – This tells you the number of protons in an atom of an element – This also tells you the number of electrons in an atom of an element, because elements are neutral. – This IS found on the Periodic Table Atomic Mass – This tells you the mass (in grams) of one mole of atoms of an element – Can be used to determine the number of neutrons in an “average” atom – This IS found on the Periodic Table Mass Number – The total number of protons and neutrons in the nucleus is the mass number of the atom. – This is NOT found on the Periodic Table Confusing Terms!

We will use what we learned here to determine the number of particles in atoms and isotopes of elements. What’s Next?