What are objects around us made of?

1. What are objects around us made of? Objectives:At the end of this lesson, students must be able to know and explain the following: • What are the basic units of chemistry and how do we represent them? • What information is contained in the periodic table? • Bohr’ atomic model • Describe using your own words what have been covered

2. Introduction What is Water? Water covers 75% of the earth's surface and every living organism depends on water for survival.  We all know water when we see it, and most people can even recite its molecular formula - H2O.  But what does that mean?  And how does the chemistry of water relate to water's properties?  This lesson will discuss molecules, atoms, and subatomic particles - the building blocks of chemistry.  Later in the course, we will discover how the chemical properties of water produce its unique characteristics. 

3. Building Blocks of Chemistry In chemistry, as in any other discipline, a series of progressively smaller substances make up an object.  However, in contrast to some other disciplines, the building blocks of chemistry are harder to visualize because they are too small to see with the naked eye and are often too small to see through a microscope.  This section will briefly present the main building blocks of chemistry to give you a frame of reference for the rest of the lesson.  If you were building a house, you might do so by stacking up concrete blocks - the primary building blocks of the house.  A lake is made in a similar manner by stacking up water molecules.  The water molecule is the smallest unit of water which retains its unique properties. 

4. Water as an example

5. Real life example • If you look closely at a concrete block, you will notice that it is, in turn, made up of small chunks of concrete along with some chunks of gravel.  If you had a bucket of these little concrete and gravel chunks, they wouldn't be much use for building a house, but they can combine into the useful concrete block.  • A molecule can also be broken down into smaller parts, called atoms, which have different properties than the molecule.  In the case of water, each molecule is made up of one atom of oxygen and two atoms of hydrogen, neither of which acts like water when separate.  In fact, you breathe in oxygen constantly while breathing water would cause you to choke and suffocate. 

6. Atoms • Chemical Elements and the Atom • All things are made up of a substance called matter. You can think of matter as everything that is not empty space. Many people believe that the space around them is empty space. • All matter, including the air we breathe, is composed of very tiny, basic units called atoms. An atom is composed of three types of subatomic particles: protons, electrons and neutrons.

7. Charges of Sub-atomic particles • A proton is a positively charged particle, whereas a neutron is a particle that does not have a charge, or neutral. • The number of protons in the nucleus equals the number of electrons in an electrically stable atom. • Electronsare found in the electron cloud, have a negative charge, and have such a tiny mass that it is negligible. 

8. The Atom

9. If everything is made up of atoms, then how can all matter be so different? • Atoms can have different numbers of protons, electrons, and neutrons. These different numbers of subatomic particles define the different elements. • An element is a pure substance made up of only one kind of atom. Examples of different elements include Hydrogen, Carbon, Sulfur, Oxygen, Nitrogen and Phosphorus.

10. Different elements have very different physical properties or characteristics. • Atoms of the same element have the same number of protons, electrons and neutrons. • However, atoms of different elements have different numbers of protons, electrons and neutrons. • It is only the number of these subatomic particles that creates the different properties found among the elements.

11. Atom con… • Because the number of protons and electrons must be equal in all neutral atoms, the atomic number could represent either the number of protons or electrons. • Scientists have decided that the number of protons represents the atomic number, because the number of electrons may vary when atoms participate in chemical reactions.

12. Symbols used in representing atoms A: The number of Protons + Neutrons(mass number) Z: The number of Protons or atomic number A-Z: represents the number of Neutrons

13. Isotope • Atoms of the same element with the same atomic number but with different mass number

14. Question is an element with 8 neutrons in its nucleus. • What is the value of Z if A is 16? • Can A be equal to 17? Give reasons • Can Z have different values of the same element? Explain

15. The Periodic Table There are many different kinds of atoms, known as different elements.  • All atoms of a certain element have identical chemical properties.  So, any two oxygen atoms will behave identically.    • Each element is distinguished by the number of protons (known as the atomic number) in each atom's nucleus.  • For example, an atom of the element hydrogen has one proton in its nucleus while an atom of the element oxygen has eight protons in its nucleus

16. The Periodic Table

17. PT con…. • The periodic table, shown, lists all of the known elements in the order of their masses.  • As you can see, the table begins at the top with the lightest element, hydrogen (H), and ends with the heaviest element, Meitnerium (Mt).  • Each box contains the element's atomic number as well as its name, abbreviated into a one or two letter symbol.  • For example, table above shows that chlorine (abbreviated as "Cl") contains 17 protons within each atom, making it heavier than sulfur (S) and lighter than argon (Ar.)  • You will notice that the elements on the periodic table are broken into several rows of different lengths.  • The table has been arranged so that elements with similar properties are found in the same column of the table.  For example, two common causes of hardness in water - magnesium (Mg) and calcium (Ca) - are both found in the same column.

18. Metals, Nonmetals, and Metalloids • The periodic table is divided into three main sections based on the properties of the elements.  As you can see on the table in the last section, the majority of the elements are classified as metals, which are good conductors of heat and electricity, often have a shiny appearance, and are usually solids at room temperature.  • Nonmetals make up a smaller proportion of the periodic table but contain many of the elements we will deal with in this course.  Nonmetals are poor conductors of heat and electricity.  • Finally, metalloids have some of the characteristics of metals and some of the characteristics of nonmetals.  They tend not to be shiny and flexible like metals, but they can conduct some electricity. 

19. Atomic Mass and Atomic Number All elements can be identified by their atomic mass and atomic number. These two values can tell you how many protons, electrons, and neutrons are in any element.. • Hydrogen has one proton and one electron. It has an atomic number of one and an atomic weight of one.

20. Oxygen • Oxygen has eight protons, eight electrons, and eight neutrons. It has an atomic number of eight and an atomic weight of sixteen.

21. The Bohr Model of an atom A physicist, Neils Bohr, designed a model for atomic structure. • It is called the Bohr model and is a simple but excellent way to visualize the structure of atoms. • The Bohr model describes the protons and neutrons located at the center of the atom, in what we term as the nucleus. The electrons exist around the nucleus in what we call electron shells.

22. The term electron shell (or energy levels) describes where electrons are located. • A nucleus can have seven shells, but most chemicals contain electrons in the first four, which are labeled the K, L, M and N shells. • The K shell is the closest to the nucleus and the N shell is the farthest from the nucleus. These shells contain different numbers of electrons. • The maximum number each shell can hold is equal to 2N2, where N is the number of the shell (K=1, L=2, M=3, N=4).

23. Bohr’ model of an atom

24. Question: Fill in the missing information

25. Questions • What are the basic building blocks of matter? • What are the information we can find from the periodic table • Draw a Bohr’s atomic model representing an element calcium • Explain the concept of an “isotope” • Which of the following cannot be isotopes? Give reasons:

26. Questions con… • A given isotope has a mass number of 196, and 60.2 % of the nucleons are neutrons. How many electrons are in the cation of this element if it has a charge of “2”? • Describe using your own words to the class what have been covered in this lesson

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