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Chemistry

Chemistry. DI Biology Jennifer Naples. Elements. An element is a substance that can not be broken down into smaller substances There are 90 naturally occurring elements in nature All elements are listed in the periodic table. Periodic Table of Elements. The periodic table of elements.

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Chemistry

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  1. Chemistry DI Biology Jennifer Naples

  2. Elements • An element is a substance that can not be broken down into smaller substances • There are 90 naturally occurring elements in nature • All elements are listed in the periodic table

  3. Periodic Table of Elements • The periodic table of elements

  4. Elements • There are 25 elements needed for all living things • 96% of the mass of human beings is: • Carbon • Hydrogen • Oxygen • Nitrogen

  5. Atoms • An atom is the smallest part of an element • There are 4 parts in the arrangement of an atom • Nucleus - the center of an atom • Proton - (+)charged particle found inside of the nucleus • Electron-(-)charged particle found outside the nucleus • Neutron – Particle found inside the nucleus with NO charge

  6. Energy Levels • Regions where electrons travel around the nucleus • Each energy level can hold a certain number of electrons • 1st energy level can hold 2 electrons • 2nd level can hold 8 electrons • 3rd energy level can hold 18 electrons • All energy levels must be used in order for an element to be stable

  7. Example • If an element has 8 total electrons, two will be in the first energy level and the remaining 6 will be in the second level. • Is this element stable? • NO! The second shell is not full • How many electrons would this element need in the second energy level to be stable? • 8

  8. Electron Configuration • Draw the electron configuration for an atom that has 9 electrons. Is it stable? • Draw the electron configuration for am atom that has 16 electrons. Is it stable?

  9. Atomic Number • The number found above an element on the periodic table • Is equal to the total protons in the nucleus • Also indicates the number of electrons since protons and electrons always equal one another

  10. Determining the Number of p+, n and e- • Protons are always equal to the atomic number • Carbon’s atomic number is 6=6 protons • Electrons are also equal to the atomic number • Unless it is an ion(+ or – charge) • Neutrons=atomic mass - atomic number • Carbon = 12 atomic mass, 6 atomic number = • 6 neutrons

  11. Practice Problem • Find the number of protons, neutrons and electrons for helium: • 2 protons, 2 neutrons, 2 electrons

  12. How Elements Combine • Compound – a substance that is made from two or more different elements bound together • Example: Salt(NaCl) or water (H2O) • Molecule – a group of atoms held together by covalent bonds • Example: oxygen (O2)

  13. Ions • Sometimes atoms have a charge • The charge can be either positive or negative • An ion is created when an atom gains or loses an electron • This charge changes the # of subatomic particles in the element • Example: • Na+2

  14. Ions • Figuring out the number of P,E and N in an ion: • First figure out the structure for the atom • Change the # of electrons according to the charge listed near the element • K+2 • K has 19 electrons • K+2 has a +2 positive charge • Take AWAY 2 electrons • K+2 has 17 electrons

  15. Ions • Try it yourself: • Find the number of electrons for N-1 • What is the number of electrons for N? • 7 • What is the number of electrons for N-1

  16. Compounds and Bonding • Compound – a substance composed of elements that are chemically combined • What does it mean to be chemically combined • Chemical vs. Physical change

  17. Compounds and Bonding • Why do elements combine? • Electrons surround the nucleus in energy levels • In order to be stable the outer valance shell must be filled • The pull on an atom on another electron is known as electronegativity • More electronegativity=more pull on electrons

  18. Covalent Bonds • When two atoms share electrons • Example: water • Strong bonds • Most living things are made • Up of covalent bonds

  19. Ionic Bonds • When two elements of opposite charge combine. • An ion is an atom that has acquired a positive or negative charge • Example: Na+Cl = NaCl • Weak bonds

  20. Chemical Reactions • When they occur: • Bonds are formed • Bonds are broken • Substances are changed or altered into different substances

  21. Metaboliosm • Refers to the chemical reactions that take place within an organism

  22. Chemical Equations • Reactants – substances that undergo the reaction • Products – substances which are formed from a reaction • Subscripts – The number of atoms of each element in a molecule • Coefficient – The number before each chemical formula(number of molecules of that substance)

  23. Examples of Chemical Equations • Water

  24. pH • pH – refers to the hydrogen ion (H+) versus hydroxide ion (OH-) concentration in a solution • Acid – a substance that has more H+ ions and has a pH BELOW 7 • Base – a substance that has more OH- ions and has a pH ABOVE 7

  25. pH Scale

  26. pH Examples • Pure water has a pH of 7.0 which means it has a equal amount of H+ and OH- ions • Hair remover(Nair) has a pH of 13.0 • Soda has a pH of 3.0

  27. Ionization • When a nonionic compound is converted into ions • Water can go through this process. Water can be converted into H+(Hydronium ions) and OH-(Hydroxide ions)

  28. Atomic Mass • The number found below an element on the periodic table. • Is equal to the total protons and neutrons in a nucleus

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