Properties of Atoms & The Periodic Table Chapter 17 Properties of Atoms & The Periodic Table

BellWOrk- 2/6-2/7 What is the difference between a compound and a mixture? What is the difference between a physical change and a chemical change and give an example of each.

BellWork-2/8-2/9 Draw Lewis Dot Diagram for each Element (Electron Dot Diagrams) 1. Neon 2. Carbon 3. Potassium 4. Bromine

Section 1: Atomic Structure

Atomic Components All elements are composed of atoms, which are the smallest pieces of matter that still retain the property of the element. Atoms are broken down into even smaller particles, called protons, neutrons, and electrons

Atomic components Protons and neutrons are found in the center of the atom, called the nucleus Protons are particles with an electrical charge of +1 Neutrons are particles that do not have an electrical charge Question: What overall charge will the nucleus have?

Scientists currently know there are 6 unique quarks: Atomic components Protons and neutrons are made up of even smaller particles called quarks Scientists currently know there are 6 unique quarks: One arrangement of 3 gives us a proton, while a different arrangement of 3 gives us a neutron

Atomic components Surrounding the nucleus is a cloud of electrons, which are particles with an electrical charge of -1. Electrons are much smaller than protons and neutrons Question: What overall charge will the atom have?

Section 2: atomic models

Dalton’s model In the 1800s, John Dalton offered proof that atoms do in fact exist. His earliest model of the atom was a solid sphere, like the one shown below. As you will see, we use a very different model today

Electron cloud model In the early 1900s, scientists developed the electron cloud model The electron cloud is the area around the nucleus of an atom where the electrons are most likely found.

Electron cloud model The electron cloud is 100,000 times larger than the diameter of the nucleus Electrons are very small and move very quickly around the nucleus. This makes it impossible to know the exact location of the electrons in the atom, so we just say they are in the electron cloud

That’s how we got these…

Electron cloud structure Not all electrons are the same, though Scientists have found that electrons in the cloud have varying amounts of energy

Electron cloud structure The energy differences can be displayed by putting the electrons in energy levels surrounding the nucleus

Electron cloud structure Energy levels closest to the nucleus have lower energy than those farther away The lowest levels are filled first, then the outer levels are filled

Electron cloud structure The maximum number of electrons that can be contained in each level is shown in the diagram to the left The 2nd shell is important for classification purposes later in the chapter

Section 3: atomic mass

Atomic mass The nucleus makes up most of the mass of an atom because protons and neutrons are far larger than electrons

Atomic mass The unit of measurement we use for atomic particles is called the atomic mass unit, or amu Protons and neutrons each have a mass of approximately 1 amu Electrons are so small we can neglect them

The number of protons in an atom is what we call its atomic number # protons = atomic number For example, all Carbon atoms have 6 protons, so the atomic number for Carbon is 6 Another way to say that, Carbon has an atomic number of 6, so Carbon atoms have 6 protons

Mass number The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus Protons + Neutrons = mass number back to the Carbon example: there are 6 protons and 6 neutrons. What is the mass number of Carbon?

If you know the mass number and the atomic number, you can find out! Atomic & mass number Say you want to find the number of neutrons in an atom. How would you go about doing that? If you know the mass number and the atomic number, you can find out! # neutrons = mass number – atomic number

Number of Electrons is… By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.

practice An element has 8 protons. What is the atomic number? If the mass number is 16, how many neutrons are there? Thought Question: if there are 8 protons, how many electrons will there be? [think about the overall charge of the atom]

How to find that on the periodic table Top: atomic number Middle: element symbol and name Bottom: atomic mass

isotopes Atoms of the same element that have a different number of neutrons are called isotopes. You use the mass number to determine whether an atom is an isotope or not For example: 2 Boron atoms are shown, and the mass numbers are different Subtract the atomic number from the mass number and you will have the number of neutrons

Section 4: the periodic table

Organizing the elements Where do we find information on all of the elements? “periodic” means “repeated in pattern” Dmitri Mendeleev was a Russian chemist who came up with a way to organize the elements so that it was easy to find information about them

Organizing the elements Mendeleev noticed a particular pattern, so he arranged the elements known at that time by increasing atomic mass In 1913, Henry G.J. Moseley’s work led to the arrangement we use today In the periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties Smaller atomic #  larger atomic #

Organizing the elements

Organizing the elements The vertical columns (up and down) in the periodic table are called groups or families, and are numbered 1 – 18 Elements in each group have similar properties

Organizing the elements

Organizing the elements A complete and stable 2nd electron shell (which we will call the outer shell) will contain 8 electrons Elements in the same group will have the same number of electrons in the outer shell

Organizing the elements Elements want 8 electrons in their outer shells 8 electrons in the outer shell = happy element!!   

Organizing the elements Remember: if there are 8 protons in an atom that is not an isotope, how many electrons will there be? The atomic number = number of electrons

Organizing the elements First row: hydrogen has 1 atom in the first shell Helium has 2, so it is full and complete Second row: lithium has 2 electrons in the first shell, and 1 in the second shell So on, until there are 8 in neon’s shell

Organizing the elements Each row ends when an outer level is filled with 8 electrons This is so important, they have developed a way to diagram them

Electron Dot diagrams

Electron dot diagrams Elements that are in the same group have the same number of electrons in their outer energy level An electron dot diagram uses the symbol of the element and dots to represent the electrons in the outer energy level These diagrams are used to show how the electrons in the outer energy level are bonded when elements combine to form compounds

Electron dot diagrams Let’s draw the electron dot diagram for Carbon

Let’s practice Draw the electron dot diagrams for Li, Be, B, C, N, O, F, and Ne