Atoms and Their Structure Chapter 4

Atoms Elements are made of particles called atoms Atoms are the smallest pieces of matter that contain all the properties of a specific element Each element contains only one type of atom

Essential Question How do we know what the atom looks like when no one has ever seen it?

Inside the Atom Atoms are made up of smaller particles These particles are found in different regions of the atom

Protons Positively charged particles found in nucleus of atom Have an electrical charge of +1 Mass of 1 a.m.u. Composed of quarks

Neutrons Neutral particles found in nucleus of atom Have no electrical charge Mass of 1 a.m.u. Composed of quarks

Electrons Negatively charged particles found in electron cloud Have an electrical charge of -1 Constantly moving around outside nucleus Have essentially no mass

Nucleus The nucleus is the positively charged dense core in the center of the atom Contains 99.9% of mass of atom Houses protons and neutrons

Electron Cloud Region around nucleus Houses electrons

Atomic Models Have been revised many times to explain new discoveries Democritus (4 th century B.C.) first theory - thought the atom could not be split Theory was modified when subatomic particles were discovered

Newer Models Bohr’s Model (1913) revised earlier thoughts –Showed electrons moving in paths like planets Revised in 1925 –Now electrons in cloud Quantum Mechanical Model

Valence Electrons Electrons in the outermost energy level of an electron are called valence electrons These are the electrons furthest from the nucleus

Atomic Number & Mass Number Atomic number = # p + –For atoms atomic number also = number of e- Mass number = # p + + # n 0 –Mass number is a whole number –Number on the periodic table is average atomic mass (not a whole number) How can you solve for numbers of neutrons?

How Atoms Differ: Ions and Isotopes Usually by way of differing numbers of p +, n 0 and e - –Different elements have different numbers of p + –Ions have charges the number of e- ≠ number of p+ charge = # p + - # e - –Atoms with the same number of p + but different number of n 0 are isotopes. Mass number of isotopes of the same element changes

Symbols of Ions and Isotopes For ions chemists use the following notation: Or just:

For isotopes chemists use the following notation: Name of element – mass number Examples: carbon-12 carbon-14 uranium-236

Determine the Numbers of p +, n 0, and e - for the following symbols given: calcium - 46 nickel - 60

Radiation Unstable Nuclei & Radioactive Decay

Early Pioneers in Radioactivity Roentgen: Discoverer of X-rays 1895 Becquerel: Discoverer of Radioactivity 1896 The Curies: Discoverers of Radium and Polonium Rutherford: Discoverer Alpha and Beta rays 1897

What do we mean by Radioactivity? Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. There are numerous types of radioactive decay. The general idea: An unstable nucleus releases energy to become more stable

Nuclear Reactions vs. “Normal” Chemical Reactions Nuclear reactions involve the nucleusNuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearrangedThe nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energyThe opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons“Normal” Chemical Reactions involve electrons, not protons and neutrons

Types of Radiation Alpha (  ) – a positively charged helium isotope –we usually ignore the charge because it involves electrons, not protons and neutrons Beta (β) – a fast moving (high energy) electron Gamma (γ) – pure high energy; called a ray rather than a particle

Other Nuclear Particles Neutron Neutron Positron – a positive electron Positron – a positive electron Proton – usually referred to as hydrogen-1Proton – usually referred to as hydrogen-1 Any other elemental isotopeAny other elemental isotope

Three Common Types of Radioactive Emissions Alpha Beta Gamma