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8th Grade Science Chemistry Concepts Atoms Objectives 1. Compare the charge, location and relative mass of protons, neutrons, and electrons. 2. Calculate the number of particles in an atom using the atomic number, mass number, and overall charge. 3. Calculate the atomic mass of elements. All substances are composed of elements Elements are pure substances that cannot be broken down into simpler chemical substances. What’s the Matter? • The smallest particle that an element can be broken down into and still be that element is called an atom. • Atoms are the building blocks of all matter. – Matter is anything that has mass and volume • Atoms cannot be seen – even with a microscope! They average about 300/1,000,000 cm in diameter. • It would take 50,000 aluminum atoms to equal the thickness of sheet of foil! Atomic Structure • An atom has a small positively charged center surrounded by a large region with negatively charged particles Atomic Structure • An atom is made up of three main smaller particles called subatomic particles. • These are protons, neutrons, and electrons. • Each of these has a specific location, charge and mass Atomic Structure • The center of an atom is called the nucleus. • Inside the nucleus are two types of subatomic particles: protons and neutrons. • The nucleus makes up 99% of an atoms mass • 1/100,000 the diameter of the atom nucleus P For Positive! • Protons are positively charged particles in the nucleus. • All protons are identical to each other. • Mass of a proton = 1.7 x 10-24g = 1 atomic mass unit (amu) • Made of three smaller particles called quarks. N Is For Neutral! • Neutrons are particles in the nucleus of an atom that have no charge (neutral) • All neutrons are identical. • Mass of a neutron = 1 amu • Made of three smaller particles called quarks. E is for Electron! • Outside the nucleus are negatively charged particles called electrons. • They are found in regions called electron clouds. • They orbit the nucleus, but not in definite paths. • Mass is so small it is considered zero Nucleus contains Protons -positive p+ Electrons -carry a negative charge e- Neutrons -neutral n0 Electrons, Protons, & Neutrons: Why are they important? • The number of protons in an atom tells you what element it is: carbon, silicon, etc. • The number of protons an element has is called the atomic number. • Every element has a unique number of protons. 1 proton Hydrogen H 6 protons Carbon C 7 protons Nitrogen N 8 protons Oxygen O Electrons, Protons, & Neutrons: Why are they important? • Atoms of the same element (same number of protons) may have different numbers of neutrons. • These atoms are known as isotopes, and share similar chemical and physical properties • There are at least 2760 naturally occurring isotopes; tin has 38! Electrons, Protons, & Neutrons: Why are they important? • The neutrons and protons make up most of the mass of an atom. This combined mass is called the mass number. • The average of the masses of all naturally occurring isotopes is called the atomic mass. Electrons, Protons, & Neutrons: Why are they important? • The number of electrons in an atom is equal to the number of protons. • Therefore, overall atoms have no net charge – they are neutral. • An atom that is not neutral is called an ion. – Positive ion (cation) = more protons than electrons – Negative ion (anion) = more electrons than protons Let the force be with you! • Objects that have the same charge repel each other, while objects with opposite charges attract each other. • This is due to the electromagnetic force. • The electromagnetic force keeps electrons around the nucleus because they are attracted to the protons (opposites attract!) • The strong force overcomes the electromagnetic force and keeps protons in the nucleus close together.