Presentation on theme: "Section 2: Masses of Atoms"— Presentation transcript:
1 Section 2: Masses of Atoms Chapter 17: Properties of Atoms
2 Warm-Up:Which of the following can change within an element and not change the identity of that element?ProtonNeutronElectron
3 Learning Goals Compute the atomic mass and mass number of an atom. Identify the components of isotopes.Interpret the average atomic mass of an element.
4 Atomic Mass The nucleus contains most of the mass of the atom. Protons and neutrons are far more massive than electronsThe mass of a proton and a neutron is almost 1 atomic mass unit (amu)
5 Atomic MassDifferent elements are distinguished by the number of protons that their atoms haveEvery carbon atom has six protonsEvery oxygen atom has eight protonsAtomic Number: the number of protons in an atom
6 Atomic MassMass Number: the sum of the number of protons and the number of neutrons in a single atomIf you know the mass number and the atomic number, you can calculate the number of neutrons# of neutrons = mass number - atomic number
12 IsotopesBecause most elements have more than one isotope, each element has an average atomic mass.Average atomic mass: the weighted average of mass of the mixture of its isotopesThe average atomic mass for each element is listed in the periodic table!
13 IsotopesFour out of every five atoms of boron are boron-11 and one out of every five are boron-10.11111111104/5(11 amu) + 1/5(10 amu) = 10.8 amu
14 Check-In:What is the mass number of an isotope of neon (Ne) that has 11 neutrons? What is the average atomic mass of neon?