Atomic Structure and the Periodic Table Chapter 10

10:1 Structure of the Atom Learning Targets: To understand atomic structure. Success Criteria: I can… list the names and symbols of common elements. describe the present model of the atom. describe how electrons are arranged in an atom.

10:1 Structure of the Atom Chemical Symbols: A chemical symbol is an abbreviated way to write the name of an element. They consist of at least one capital letter, and may also include one or two small letters. Most elemental chemical symbols match the word. Others are derived from a latin word, applied to the same element. Can you think of 10 chemical symbols? Some symbols include: H: Hydrogen O: Oxygen C: Carbon N: Nitrogen

Matter and Atoms: We already know that atoms are the basic building blocks of matter. What is an atom made of?

Atoms are made of: Nucleus: The center Protons: positively charged particle Neutron: negatively charged particle Electron Clouds: Inhabited by electrons, outside the nucleus. Electron: Negatively charged particle.

The most defining characteristic of an atom is its atomic number. Atomic number is the number of protons in the nucleus. Every atom of the same element contains the same number of protons. Example: All hydrogen atoms have 1 proton, while all helium atoms have 2. In a stable (neutral atom), how many electrons would there be if it has 3 protons? Since “neutral” means no charge, you have to cancel out each proton with an electron. A neutral atom with 3 protons would also have 3 electrons.

Models of Atoms: Over the years, there have been a few accepted models of what the atom looks like. Models: Bohr Model: Electrons orbit the nucleus in distinct, clear paths.

Electron Cloud Model Electrons move around in an electron cloud. This is where an electron is most likely to be at any time. Electron clouds represent the probable locations of electrons within an atom.

Energy Levels of Electrons: Although we can say with certainty that electrons are orbiting the nucleus, it is impossible to pinpoint exactly where they are at any given time. We can, however, predict where they will most likely be. Within the electron cloud, electrons can be found at various distances from the nucleus on shelves called orbitals. Electrons near the nucleus have low energy. Electrons farther from the nucleus have higher energy.

Electron cloud orbitals do have different maximum quantities of electrons that can be held. *You need to memorize the numbers associated with the first 4 orbitals.

So… Let’s apply what we know! Do this together. The helium atom has 2 electrons. What does this look like? You do: What should an oxygen atom look like? Hint: Atomic Number = 8

Learning Checkpoint: Write the chemical symbols for the elements carbon, aluminum, hydrogen, oxygen, and sodium. List the names, charges, and locations of three kinds of particles that make up an atom. What does an electron cloud represent? If you know the number of protons in an atom, what else do you know about it? When a glass rod is rubbed with a silk cloth, the rod becomes positively charged. What type of particle in the atoms in the rod has been removed? Make a concept map for the parts of an atom. Include the following terms: electron cloud, nucleus, electrons, protons, and neutrons. Also, provide the charge of each applicable part.

10:3 Masses of Atoms Learning Target: 1To understand atomic characteristics. Success Criteria: I can… 1. compute the atomic mass and mass number of an atom. 2. identify and describe isotopes of common elements. 3. interpret the average atomic mass of an element.

10:3 Masses of Atoms Atomic Mass (In general): The atomic mass unit (u) is the unit of measurement of mass in an atom. This is derived from a carbon atom. Every proton and neutron has a mass of 1 u.

Boron: Atomic #: 5, Mass #: 11 Neutrons: ? Mass Number: The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus of an atom. What does this mean? # neutrons + #protons = mass number. If you know the mass number and atomic number of an atom (see periodic table lesson), you can then calculate the number of neutrons. Mass number – atomic number = # neutrons Let’s try this! Boron: Atomic #: 5, Mass #: 11 Neutrons: ? Copper: Protons: 29, Neutrons: 34, Atomic #: ?, Mass #: ?

Not all the atoms of an element have the same number of neutrons… Isotopes: Not all the atoms of an element have the same number of neutrons… When atoms of the same element have differing numbers of neutrons, these atoms are called isotopes. Some isotopes are unstable (radioactive), but most are not.

Since most elements exist with more than one isotope, you often see atomic mass as a decimal. The average atomic mass of an element is the average mass of the mixture of its isotopes. Example: 4 of 5 boron atoms are boron-11 and 1 of 5 boron atoms are boron-10. Averaged out, the atomic mass of boron is 10.8 u.

Learning Checkpoint: A chlorine atom has 17 protons and 18 neutrons. What is its mass number? What is its atomic number? How are the isotopes of an element alike and how are they different? Chlorine is used to treat most city water systems. The atomic number of chlorine is 17. The two naturally occurring isotopes of chlorine are chlorine-35 and chlorine-37. The average atomic mass is 35.45 u. Why does this indicate that most chlorine atoms contain 18 neutrons? An isotope of phosphorus used to treat bone cancer is phosphorus-30. Another isotope is phosphorus-31. What are two reasons why most of the phosphorus in your food must be phosphorus-31 and not phosphorus-30?

10:4 The Periodic Table Learning Target: To understand how to find information in the Periodic Table. To understand how elements are grouped in the Periodic Table. Success Criteria: I can… describe the periodic table of elements and use it to find information about an element. distinguish between a group and a period. use the Periodic Table to classify an element as a metal, nonmetal, or metalloid.

10:4 The Periodic Table Produced in the 19th Century by Dimitri Mendeleev, the periodic table organizes the elements. He organized the elements by atomic number and discovered that there was a pattern to the properties of the elements. (The pattern was periodic) The Periodic Table of Elements arranges the elements according to repeated changes in properties.

Mendeleev used the visible patterns with known elements to predict the way unknown ones would behave. Scientists later discovered elements that fit into place perfectly, and behaved as predicted. After modification by Mosley, the atoms were rearranged by atomic number, rather than by atomic mass.

In each elemental box of the periodic table, you can find information about that element. Let’s analyze a couple of these on the periodic table!

Groups of Elements: One pattern seen is that the Periodic Table contains vertical columns called groups/families. These are numbered 1-18.

Elements in each group have similar properties. This is because they have similar electron arrangements. It is the number of electrons in the outer energy level that determines the chemical properties of the element. This is such an important concept, a special way of representing outer electrons has been developed. Lewis dot diagrams use the symbol of the element and dots to represent the electrons in the outer energy level. Can you make the Lewis dot diagram for oxygen, carbon, and copper? Examples: All atoms in group 18 are called noble gases. They are very stable and don’t usually form compounds.

Horizontal rows of elements in the Periodic table are called periods. Periods of Elements: Horizontal rows of elements in the Periodic table are called periods. Check out your Periodic Table… See that stair-step line on the right?

The elements to the left of that line are metals (except hydrogen). Metals commonly exist as solids at room temperature, are shiny, and are good conductors of heat and electricity. Elements to the right of the line are nonmetals. Nonmetals are often gas at room temperature, make brittle solids, and are not good conductors of heat or electricity.

Lastly, elements in groups 3-12 are transition elements. Elements touching the stair-step line are metalloids, which have properties of both metals and nonmetals. Lastly, elements in groups 3-12 are transition elements. They are metals, but have properties not found in elements of other groups.

Learning Checkpoint: Use the periodic table to find the name, atomic number, and average atomic mass of the following elements: N, Ca, Kr, and W. Give the period and group in which each of these elements is found: nitrogen, sodium, iodine, and mercury. Write the name of each of these elements and classify it as a metal, a nonmetal, or a metalloid: K, Si, Ba, and S. What property of mercury makes it different from other metals and also makes it useful in thermometers and silent light switches?