Chapter 14 Section 14.1

14.1 Structure of the Atom We know of two different kinds of electric charge and we call them positive and negative.

14.1 Electric charge in matter We say an object is electrically neutral when its total electric charge is zero.

14.1 Inside an atom The mass of the nucleus determines the mass of an atom because protons and neutrons are much larger and more massive than electrons. In fact, a proton is 1,836 times heavier than an electron.

Force of gravity inside the atom is the weakest force Force of gravity inside the atom is the weakest force. Since particles in an atom have such small masses the force is not very significant. Gravitational Force

Electromagnetic Force The electromagnetic force is due to the charges of the protons and electrons. Protons and electrons are attracted to each other because they have opposite charges. The electromagnetic force holds the electrons around the nucleus. Electromagnetic Force

The strong nuclear force is greater than the electromagnetic force, so the nucleus stays together. This force attracts neutrons and protons to each other and works only at the extremely small distances inside the nucleus. Strongest known force in the universe. Strong Nuclear Force

The weak force is an important force in radioactive atoms The weak force is an important force in radioactive atoms. In certain unstable atoms, a neutron can change into proton and an electron. The weak force plays a key role in this change. This force is weaker than both the strong nuclear force and electromagnetic force Weak forces

14.1 How atoms of various elements are different The atoms of different elements contain different numbers of protons in the nucleus. Because the number of protons is so important, it is called the atomic number.

Atomic Number Atomic Number = # of protons # of protons = # of electrons in a neutral atom ( the atom has no charge)

Mass Number Mass number = protons + neutrons Electrons are not included in the mass # because their mass is so small.

Ions Ions are atoms that have a different number of protons than electrons ..giving them an electric charge. Positively charged ions have less electrons than protons Negatively charged ions have more electrons than protons.

14.1 How atoms of various elements are different Isotopes are atoms of the same element that have different numbers of neutrons.

14.1 Radioactivity Almost all elements have one or more isotopes that are stable. “Stable” means the nucleus stays together. Carbon-14 is radioactive because it has an unstable nucleus.

If the nucleus of an atom is unstable for any reason, the atom changes into a more stable form. Radioactivity is the process in which the nucleus spontaneously emits particles or energy as it changes into a more stable isotope. Ways to do this include: Alpha decay Beta decay Gamma decay Radioactivity