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th 8 Grade Science Democritus Around 430 B.C. (2437 years ago) the Greek philosopher first proposed the idea that all matter is formed from atoms. Dalton’s Atomic Theory English chemist that first described many of the characteristics of atoms. Continued… Dalton’s Atomic Theory 1. All elements are composed of atoms that cannot be divided. Continued… Dalton’s Atomic Theory 2. All atoms of the same element are exactly alike and have the same mass. Atoms of different elements are different and have different masses. Continued… Dalton’s Atomic Theory 3. An atom of one element cannot be changed into an atom of a different element. Atoms cannot be created or destroyed in any chemical change, only rearranged. Dalton’s Atomic Theory 4. Every compound is composed of atoms of different elements combined in a specific ratio. • All matter is made of one or more elements. Elements are pure substances that cannot be broken down by any chemical or physical means. • The atom is the smallest particle of an element. Draw this: • Atoms are composed of 3 subatomic particles called protons, neutrons and electrons. • The center of the atom is called the nucleus. It contains protons and neutrons. • Circling around the nucleus is 1 or more electrons. • Atoms are different from each other because each element’s atoms have different #s of the subatomic particles. Now create a chart that looks like this: Proton Neutron Electron • The electron is found moving around the outside of the nucleus. • The electron has a (-) electric charge. • The has a mass of 0.0005 amu. (The mass of the electron is so small compared to the proton and neutron that it is ignored.) e • Protons are located in the center core of the atom called the nucleus. • Protons have a positive electric charge (+1) • Protons (p1) have a mass of 1 amu (atomic mass units). • Protons are found in the center core of the atom called the nucleus. • Protons have a positive electric charge(+). • Protons (p+) have a mass of 1 atomic mass unit (amu). Structure / Parts of the Helium Atom Electron Neutron Proton • Neutrons are also located in the nucleus. • Neutrons are electrically neutral. They do not have a charge. • Neutrons (n0) have a mass of 1 amu. AMU = protons + neutrons + electrons The periodic table gives the following information about each element and its atoms. • Atomic Number • Atomic Mass • Element Symbol Sample Periodic Table • The symbol is an abbreviation for the name of each element. It’s either 1 or 2 letters with the 1st letter capitalized. • The atomic number is the smaller of the 2 numbers. This number tells us the number of protons and electrons in the atom. • The atomic mass # is the sum of the protons, neutrons, and electrons. • This number is used to find the number of neutrons. • Finding the Neutrons = Atomic mass (rounded) – atomic number Mass – Protons = Neutrons Practice 1. Use the periodic table to determine the number of protons, neutrons, electrons, and chemical name for the following: a. N b. Na c. Te This is a Bohr model for the atoms of the element carbon. Nucleus Shell 2 Shell 1 Electron Placement • e are not all the same distance from the nucleus. Electron Placement • e are placed in shells (energy levels) which are located at different distances from the nucleus. • The shell closest to the st nucleus is the 1 shell and can hold a max of 2 e-. • Shell no. 2 can hold a max of 8 e . • Valence shells (outermost) can hold a max of 8 e . Element Protons Neutron and Electrons Carbon 6 6 Oxygen 8 8 Two atoms are isotopes of one another when they have the same # of p+ but 0 different #s of n . Atom Name Protons Neutrons Carbon 12 6 6 Carbon 14 6 8 Example of Isotopes Neutron Proton Standard Hydrogen Hydrogen Isotope • An atom is (0) when # of e- = # of p+. The atom does not have an overall charge. • An atom becomes an ion when it either gains or loses an e . There is no longer a balance between p+ and e- and the atom is now either positively or negatively charged. • 18 vertical columns called groups or families. • Elements in each group, have similar properties and characteristics. • Elements in horizontal rows called periods. • The periodic table is divided into three different regions. • The three regions are the metals, semimetals/ metalloids, and the nonmetals including the noble gases. Metals = green, Semimetals = purple, Nonmetals = yellow/orange, Noble Gases = Blue Semimetals/ Noble (Inert) Gases • Physical properties: hardness, shininess, malleability, and ductility. • Malleable material can be pounded into shapes. • Ductile material can be pulled out or drawn into a long wire. • Metals are good conductors of heat and electricity. Most are also magnetic as well. • Located on the left of the zigzag line in the periodic table. • Why were gold and silver mad when they went to school together? • Because they were in different periods! • Lack properties of metals. • Right of the zigzag line in periodic table. • Noble gases (inert gases) located in family 18. They are stable and are not reactive with other elements. Other elements want to be like them and have their outer shell full. • Elements that form the zigzag line in the periodic table. • Most chemists agree on 6 or 7 metalloids depending on which source you use. • Semimetals/metalloids have some properties of metals and some properties of nonmetals. • One of the most important properties of semimetals/nonmetals is their varying ability to conduct electricity. I asked the guy sitting next to me if he had any Sodium Hypobromite… He said NaBrO Q: What is the show cesium and iodine love watching together? A: CsI Your teacher - Making bad chemistry jokes since 1992, because all the good ones Argon! Silver walks up to Gold in a bar and says, "AU, get outta here!" I would like to apologize for not adding more jokes... but I only update them.... periodically! • When a (0) atom gains 1 or more e-, it now has more (-) e- than (+) p+. This type of ion now has a (-) overall charge and is called an anion. • A (0) oxygen atom will often gain 2 e- to become more stable. The anion now has a charge of – 2. There are 2 more e- than there are p+. Oxygen Anion Gained Electron 8 Protons and 10 Electrons = - 2 charge Gained Electron • Some people say that anions are negative. • I don’t think anions are negative, they're just misunderstood! • Q: What did one ion say to the other? • I’ve got my ion you! • When a (0) atom loses 1 or more e-, it now has more (+) p+ than it does (-) e-. Cation = (+) charged ion. • A (0) lithium atom will often lose an e- to become more stable. The cation will have a charge of + 1. Lithium Cation Electron lost 3 Protons and 2 Electrons = +1 charge Nitrogen 14 and Nitrogen 15 atoms are used in research. Answer the following questions. • What are these two atoms called? • List the number of p+, e-, and n0 for each atom. • A neutral magnesium atom loses two electrons. What is it’s charge? www.chemicalelements.com www.chem4kids.com www.webelements.com