The Atom Electrons can be used to probe inside of atoms. Higher energy electrons can detect smaller features inside of atoms. Scientists learn about the inside of atoms by watching how electrons bounce off the atom, and by how the atom changes as a result of being hit by an electron. Atomic and Molecular Structure 1.a. – Students know how to relate the position of an element in the periodic table to its atomic number and atomic mass.

Why is an Atom defined as uncuttable? What is an Atom? Everything in nature is made of matter. Atoms are the building blocks of all matter. The atom is the smallest part of an element but still has all the chemical properties of that element. Atom in Greek means “uncuttable”. Why is an Atom defined as uncuttable? Take a pile of paper clips (all of the same size and color). Divide the pile into two equal piles. Divide each of the smaller piles into two equal piles. Repeat step 3 until you are down to a pile containing only one paper clip. That one paper clip still does the job of a paper clip (i.e., hold loose papers together). Now, take a pair of scissors and cut that one paper clip in half. Can half of the paper clip do the same job as the single paper clip? Matter = substance or substances of which any physical object consists or is composed. Ancient people had hypothesized that there was a small unit of matter that broke everything down into its simplest form – just didn’t have tools to see it. W

What does an Atom look like? An Atom is very small. It consists of a nucleus, which contains the protons and neutrons, and electrons which orbit in electron shells around the nucleus. The nucleus is very small compared to the size of the entire atom. Most of the atom is empty space!

Small Nucleus Lots of Empty Space

Even though an Atom’s nucleus is so small… Even though an Atom’s nucleus is so small….it contains most of its MASS! Why? Because all the mass comes from the protons and neutrons! Electrons are so tiny very little mass comes from them….so scientists just calculate the protons and neutrons to determine atomic mass.

What makes up an Atom? An Atom is made up of 3 Subatomic Particles. Proton – positive charge Neutron – no charge Electron- negative charge Protons and neutrons about the same size and are located in the nucleus. Electrons are very small and move around the atom in electron shells.

Atoms to Elements All elements are made up of their own unique atom. Element - a material which cannot be broken down or changed into another substance using chemical means. What’s an Element? Elements are made up of lots of the same type of Atom! What elements do you Know?

Hydrogen 1 Proton 2 Protons Helium 3 Protons Lithium Beryllium Each element has its own unique number of protons. So…..the number of protons in an atom gives us the identity of the element! Hydrogen 1 Proton 2 Protons Helium Number of Protons and Electrons gives an atom its physical properties (like color, smell, hardness) and chemical properties (like reactivity). 3 Protons Lithium Beryllium 4 Protons

Elements to the Periodic Table Periodic Table – A tabular arrangement of the elements according to their atomic numbers so that elements with similar properties are in the same column. The Periodic Table was invented in 1869 by Dmitri Mendeleev. Why do you think Mendeleev left blanks in the First Periodic Table?

Periodic Table Basics NOT MASS! Periodic Table: Arranged by atomic number Has 18 vertical columns or families Has 7 horizontal rows or periods Elements in columns have similar properties Elements in rows are NOT ALIKE! NOT MASS! Periodic Table is an essential tool for scientists. It helps them understand how an element will react, what its physical properties are, and if it can conduct electricity.

Chemistry - Shearer - Standard 1 Groups or Families 1 18 2 13 14 15 16 17 3 4 5 6 7 8 9 10 11 12 Chemistry - Shearer - Standard 1

Chemistry - Shearer - Standard 1 Periods or Rows 1 2 3 4 5 6 7 Chemistry - Shearer - Standard 1

Mendeleev’s Arrangement Approximately 92 naturally occurring elements The rest are made in labs or short-lived Lightest Element = Hydrogen (#1) Heaviest Element = ununoctium (#118) Mendeleev’s Arrangement Modern Arrangement Heaviest in nature is Uranium #92. The heaviest element in terms of heaviest per a given number of atoms is the element with the highest atomic weight. This is the element with the largest number of protons, which is presently element 118, ununoctium. When a heavier element is discovered (e.g., element 120), then that will become the new heaviest element. Ununoctium is the heaviest element, but it is man-made. The heaviest naturally-occurring element is uranium (atomic number 92, atomic weight 238.0289).

How many Neutrons does Calcium have? Atomic Number = number of protons In a neutral atom (no charge), the number of protons (+) always equals the number of electrons (-)! Atomic Mass = number of protons + neutrons To find out how many neutrons an atom has just subtract the atomic mass from the atomic number! 20 How many Neutrons does Calcium have?

Chemistry - Shearer - Standard 1 The Atom Question: You have 2 identical containers. One is filled with hydrogen gas and the other is filled with oxygen gas. The containers are not labeled. How could you tell which one is filled with oxygen? (They have the same number of gas molecules in each container.) Hint: How are hydrogen and oxygen atoms different? Chemistry - Shearer - Standard 1

Chemistry - Shearer - Standard 1 The Atom Answer: Both containers have the same number of gas molecules, but they differ in the type of atom they contain. Hydrogen has only 1 proton in its nucleus. Oxygen has 8 protons and 8 neutrons. Oxygen is 16 times heavier than hydrogen. The heavier container is oxygen and the lighter is hydrogen. Chemistry - Shearer - Standard 1

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