Atoms What is the nature of matter? Salt can be divided into piles. Is there a point where salt can not be split any further? So…what is an Atom? • From Greek word “atomos” meaning unable to cut • Atom = basic unit of matter diameter = 1 That’s pretty small! pm (picometer) ~ 10 -12 A Brief History: • Democritus (4th Century BC) – First named the “atom” – Lacked evidence • John Dalton (1766-1844) – Performed experiments to discover: • Dalton’s Atomic Theory Dalton’s Atomic Theory Um, who I’m Oxygen. is this? It sure is 1. All composed of tiny I amindivisible different Heelements looks nice particles from you, but pretty called atoms. hanging Tell me I’m sure we different out with about it, could find from you you, Carbon! some way to and me, 2. Atoms of the same element are identical Carbon. bond! Carbon. Still more of Dalton’s Atomic Theory… 3. Atoms of different elements can physically mix together or can chemically combine to form compounds. 4. Chemical reactions occur when: – atoms are separated, joined or rearranged; – however, they are never changed into atoms of another element. Reflecting on Dalton’s Theory Most of Dalton’s theory is still accepted. Which part do you think has been rejected? The Atom is Divisible! Return to Theory #1 and cross out the word “indivisible” The three kinds of subatomic particles 1. Protons (p+) – – – - One unit of positive charge Relative mass = 1 AMU Actual mass = 1.67 x 10-24 grams Found in the nucleus of the atom 2. Neutrons (n0) – – – – No charge Relative mass = 1 AMU Actual mass = 1.67 x 10-24 grams Found in the nucleus of the atom The three kinds of subatomic particles 3. Electrons (e-) – – – – Negative charge Relative mass = 1/1836 AMU Actual mass: 9.11 x 10-28 grams Found in the orbitals outside the nucleus In 1911, Rutherford performed an experiment: What did this prove? Source of alpha particles Thin sheet of gold foil Atoms are mostly empty space • Rutherford proposed that the atomic structure was like “planets around the sun” – This did not account for very specific traits that atoms possessed. Atomic Structure Protons and Neutrons make up the nucleus Electrons spin around in orbitals surrounding the nucleus What makes atoms different from each other, if they have the same basic parts? The Atomic Number Definition: The number of protons in the nucleus of an atom, which also identifies the element Mass Number • The total number of protons and neutrons is called the mass number. Based on this nucleus, what is the mass number? 4 + + What element is it? Helium Atomic Number vs. Mass Number The Mass Number = the total # of p+ and no The mass number is here. The atomic number = the number of protons Usually the # of p+ = # of e2 He 4. 00 Helium Why protons? Why not neutrons? Or electrons? • Oxygen’s Atomic Number is 8. – How many protons does it have? _______ 8 8 – How many neutrons does it have? ________ 8 – How many electrons does it have? ________ Electron Orbitals • The 1st orbital of an atom (closest to the nucleus) can hold 2 electrons • The 2nd orbital of an atom can hold up to 8 electrons = octet rule The Atomic Number Element’s Name Atomic Mass 5 5 P = _____ B 6 N = _____ Boron 10.81 5 E = _____ Bohr Diagram Lewis Structure Valence Number: 3 B were HiYou there! Greetings, Nitrogen. Bonding and Chemical right! I am We are Hydrogen I’mReactions now Ammonia! atoms. Perhaps we Nitrogen. But, am I an •willChemical Bonding: change the way Am I an atom or a you think about Combining Atoms of Elements to form atom or a compound yourself. Chemical Compoundscompound? now? Oh, you can’t be serious! Chemical Symbols of Elements 1st Letter of Symbols are Capitalized Ex. C = Carbon Ca = Calcium S = Sulfur Si = Silicon Bonding An atom is most stable when its outer orbital is either full or empty To do this, it will either gain, lose or share electrons. Ionic Bonding A bond that involves a transfer of electron Ex. Sodium Chloride (NaCl) = Salt! Na+1 ion Sodium Cl -1 ion Chlorine What keeps ionic bonds together? • One atom loses its electron, therefore becoming a positive (+) ion. • The other atom gains an electron, therefore becoming negative (-) ion. • Opposites attract! Luv ya honey! (+) Luv ya too! (-) Can you guess which Covalent Bonds element I am? will complete • A covalent bond is What a chemical bond my valence shell? formed by sharing electrons. Different types of Covalent Bonds Single Bond: One pair of shared electrons Double Bond: Two pairs = of H shared – H electrons Triple Bond: Three pairs of shared electrons O=C=O C Hydrogen Cyanide (HCN) can form this. Can you? Bonding Basics Practice 1- Ionic Bonds 1. Mg + Br 2+ Br 2. Pb + S 1- Mg 2- 4+ S Pb Br MgBr2 2- S PbS2 1- Cl 3. Al + Cl Cl Al Cl 1- 3+ 1- AlCl3 Bonding Basics Practice Covalent Bonds 1. H + Cl Cl H – Cl H Cl 2. C + Cl Cl C Cl Cl O Si Cl C Cl CCl4 Cl Cl 3. Si + O HCl O O = Si = O SiO2 How do you count atoms? H2O Subscript = # of atoms within that molecule 2 Hydrogen 1 Oxygen Al2(SO4)3 Subscript = multiple of everything within the parenthesis 2 Aluminum 3 Sulfur 12 Oxygen 3Al2(SO4)3 Number in front indicates # of entire molecular unit 6 Aluminum 9 Sulfur 36 Oxygen Chemical Equations • Chemical equations are sentences that describe chemical reactions • A chemical reaction involves the breaking and reforming of chemical bonds (rearrangement of atoms) Reactants (ingredients) Products (what’s made) 2 H2 + O2 2 H 2O Equations are “balanced” = same number of atoms on both sides of the arrow.