1. Unit D Chemical Interactions Chapter 1: Atomic Structure and The Periodic Table

2. Section 1.1 – Atoms are the Smallest Form of Elements All Matter is Made of Atoms How many different substances can there be? 2400 years ago, Greek philosophers proposed that everything on earth was made of only 4 basic substances – air, water, fire, and earth Today, chemists know there are about 100 basic substances – or elements that account for everything we see and touch These elements can appear alone but most often combine to make new substances

3. Types of Atoms in Earth’s Crust and Living Things Hydrogen atoms make up about 90% of the universe but they only make up about 1% of the earth’s crust but MOST hydrogen atoms are combined with oxygen atoms in the form of water. Atoms of the elements that make up living things are very different from those that make up the Earth’s crust. (see p. D10) All living things are composed of primarily oxygen, carbon, hydrogen, and nitrogen – oxygen = more than half your body’s mass

4. Names and Symbols of Elements Elements get their names in many different ways Each element has its own unique symbol For some elements it is their first letter – hydrogen (H), sulfur (S), carbon (C) Some elements use their first plus one other letter – Aluminum (Al), platinum (Pt), cadium (Cd), Zinc (Zn) Some element’s symbols are less obvious – these come from Latin names - Gold (Au), Lead (Pb), Iron (Fe), copper (Cu)

5. Each element is made of a different atom In the early 1800’s, British Scientist John Dalton proposed that each element is made of tiny particles called atoms. All atoms of particular element are identical but different from other atoms of other elements Dalton thought that atoms could not be divided into anything simpler but scientists found that atoms are made of smaller particles

6. The Structure of an Atom Atoms contain charged particles The charge can be either positive or negative Particles with the same charge repel – they push apart Particles with different charges attract each other – they are drawn to each other

7. Atoms are composed of three types of particles – electrons, protons and neutrons PROTON = Positive charge NEUTRON = Uncharged Protons and neutrons found in the nucleus of the atom – nucleus has positive charge ELECTRONS = negative charge Electrons move around outside of the nucleus in a cloud

9. Atoms are extremely small Millions of atoms could fit onto a dot-. Electrons are about 2000 times smaller than protons and neutrons Electrons move around the nucleus very quickly so it is very difficult to pinpoint their exact position = electron cloud Negative electrons are attracted to positively charged protons Negative electrons repel each other so they are spread out in the electron cloud Neutral atoms have an equal number of protons and electrons = no electrical charge

10. Atomic Numbers The identity of an atom is determined by the number of protons in the nucleus = THE ATOMIC NUMBER Hydrogen atom Atomic Number 1 = 1 proton in the nucleus Gold atom 79 protons in nucleus = Atomic Number 79

11. Atomic Mass Numbers Total number of protons and neutrons in the nucleus = Atomic Mass Number Atoms of certain elements always have the same number of protons in the nucleus but they may not always have the same number of neutrons, so not all atoms of an element have the same atomic number ISOTOPES are atoms of the same element that have a different number of neutrons

12. Example: All chlorine atoms have 17 protons (Atomic Number) Some chlorine atoms have 18 neutrons while others have 20 neutrons = chlorine isotopes How do you find the number of neutrons in an atom? Subtract the atomic number from the atomic mass number EX. Chlorine- 35 35 (atomic mass number) – 17 (atomic number/protons) = 18 neutrons EX. Chlorine- 37 37 (atomic mass number) – 17 (atomic number/protons) = 20 neutrons

13. Atoms form ions An atom has an equal number of protons and electrons = no electrical charge When an atom loses or gains one or more electrons, an ION is formed Since number of electrons do not equal the number of protons in an ion, the ion has an electric charge

14. Formation of Positive IONS When an atom loses one electron, there are more protons in the atom The ion then has a positive charge The positive ion is smaller than the neutral atom since the electron cloud became smaller when the electron was lost

15. Formation of Negative Ions When an electron is added to an atom, a negative ion is formed. The negative ion is larger than the neutral atom because the electron cloud is bigger with extra electrons (electrons repel)