How Atoms Differ

What are the subatomic particles? What are their charges? Where are they located? What are their sizes? 2

Properties of Subatomic Particles Symbol Location Relative Charge Relative mass Actual mass (g) Electron e- or In the space surrounding the nucleus 1- _1__ 1840 9.11 x 10-28 Proton p+ or In the nucleus 1+ 1 1.673 x 10-24 Neutron n0 or 1.675

What makes a carbon atom a carbon atom? What number represents the number of protons? How do we use the atomic number?

Atomic Number The atomic number is the number of protons or electrons in a neutral atom Remember that atoms are neutral thus: Atomic number = Number of protons = number of electrons Each element has a unique number of protons The periodic table is organized by increasing atomic number (number of protons) Only protons determine the type of atom present and will never change for an element.

Question Time What does the atomic number represent? Why are there an equal number of protons and electrons in a neutral atom? How many protons and electrons are in aluminum (Al)? An atom contains 28 protons, what element is it? How many electrons does it have? How is the periodic table organized? What subatomic particle determines the type of element?

How would we figure out the mass of an atom? What is something that can be different from one atom of the same element to the next? How would we figure out the mass of an atom? 8

Isotopes and Mass Number What could isotope mean? Do you know any other words that begin with iso-? Isotopes are atoms of the same element that have the same number of protons but different number of neutrons Mass number represents the sum of the number of protons and neutrons in the nucleus So, # of neutrons = mass number – atomic number

Representing Isotopes In Ag-107, the 107 represents the mass number (neutrons + protons) In Ag-109, the 109 represents the mass number (neutrons + protons) How many neutrons are there?

Question Time What are isotopes? What is the mass number? What is the mass number in carbon-14? What is the mass number and atomic number in Fe? How many protons, neutrons, and electrons are in potassium-41, whose symbol is K? How many protons, electrons, and neutrons are in Ne? What is the difference between hydrogen ( H), deuterium ( H), and tritium ( H)? 56 26 22 10 1 2 1 3 1

Could we use grams to measure the mass of an atom? What could we use? If there are multiple isotopes, how would we figure out the mass for the element?

Atomic Mass The mass of an atom is so small it is difficult to work with, so chemists have developed an atomic standard to compare all the masses to The standard is the atomic mass unit (amu) is defined as 1/12 of the mass of a carbon-12 atom If the mass of an element is not close to a whole number, it is because the atom has several isotopes The atomic mass is the weighted average of the isotopes of that element.

Example Silver has two naturally occurring isotopes. Ag-107 has an abundance of 51.82% and mass of 106.9 amu. Ag-109 has a relative abundance of 48.18% and a mass of 108.9 amu. Calculate the atomic mass of silver.

Question Time Rubidium is a soft, silvery-white metal that has two common isotopes, Rb and Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium? 87 37 85 37

Vocabulary to Know Atomic #- Mass #- Isotopes- D. Atomic mass- same # of protons & electrons protons + neutrons written 2 ways: Carbon-14 or C 14 6 same # of protons, different # of neutrons weighted average mass