Chapter 4: Elements, Atoms, and Ions Atomic Structure
Learning Goals: • Describe the components of an atom. • Distinguish between protons, neutrons, and electrons in terms of charge and mass.
ChemQuestion: • Are all atoms the same? If so, explain what they all have in common. If not, explain how they can be different.
Electrons • Discovered by J.J. Thomson • Cathode Ray Tube Experiment • Showed that atoms of any element can be made to emit tiny negative particles.
Electrons • Electrons – negatively charged subatomic particles (e-) • Located in the space surrounding the nucleus • 1 electron has a charge of -1 • Relative Mass = 1/1840 of a hydrogen atom (small enough to be negligible)
Nucleus • Discovered by Ernest Rutherford • Gold Foil Experiment • Showed that atoms have a very small, very dense center.
Nucleus • Nucleus – very small, very dense, positively charged center of the atom
Protons • Protons – positively charged subatomic particles (p) • Located in the nucleus • 1 proton has a charge of +1 • Relative Mass = 1
Neutrons • Discovered by James Chadwick • Neutrons– neutral subatomic particles (n) • Located in the nucleus • 1 neutron has a charge of 0 • Relative Mass = 1
Atoms and the Periodic Table • Atomic Number = the number of protons in an atom • For a neutral atom, it is also equal to the number of electrons.
Atoms and the Periodic Table • Atomic Mass = the sum of protons and neutrons (measured in atomic mass units, amu) • Electrons are incredibly small compared to the size and mass of protons and neutrons that they are not considered in the mass of atoms.
Check-in: • A neutral atom has 35 protons. List everything you can determine about this element.