Unit 2. Chemical Foundations: Elements, Atoms, and Ions

Transcription

1 Unit 2 Chemical Foundations: Elements, Atoms, and Ions

2 Memorize the list of elements You will have a quiz on this list. All of the elements will be on the quiz!

3 Elements in the Earth System (% mass in Crust, Ocean, & Atmosphere) Oxygen 49.5 % Silicon 25.7 % Aluminum 7.50 % Iron 4.71 % Calcium 3.39 % Sodium 2.63 % Potassium 2.40 % Magnesium 1.93 % Hydrogen 0.87 %

4 Your body is worth less than $1.00 Elements in the Human Body Oxygen 65.0 % Carbon 18.0 % Hydrogen 10.0 % Nitrogen 3.0 % Calcium 1.4 % Phosphorus 1.9 % Magnesium 0.50 % Potassium 0.34 % Sulfur 0.26 % Sodium 0.14%

5 An element is a pure substance containing only one kind of atom. An atom being the smallest unit of an element. A compound is a pure substance containing 2 or more kinds of atoms combined in definite proportions. A molecule is the smallest unit of a compound. Chemical symbol is one or two letters used to represent an element. The first letter is capitalized, the 2 nd (if one) is lower case. A subscript is a number telling how many of the atom before the number required. If there is no number, there is one atom.

6 Some elements take their names from Latin so their symbols don t seem to make sense.

7 Rules for Writing Formulas 1. Use element symbols 2. The number of each type of atom is indicated by a subscript (small number) written to the right of the element symbol 3. If only one of an atom type, the subscript 1 is not written

8 Chemical formulas Subscript H 2 O 1 molecule 2 hydrogen 1 oxygen Ag 2 CrO 4 1 molecule 2 silver 1 chromium 4 oxygen formula Na 2 CO 3 1 molecule 2 sodium 1 carbon 3 oxygen

9 Formulas using ( ) ( ) x means that anything inside ( ) needs to be taken x number of times. (NH 4 ) 2 CO 3 (1x2) = 2 N, (4x2) = 8 H, 1 C, 3 O Al 2 (SO 4 ) 3

10 Diatomic molecules There are 7 elements that do not exist as 1 atom alone. As an element, they are always as 2 atoms bonded together as a molecule. Location of the diatomic elements

11 Nuclear Notation Atomic mass = p + + n Atomic number = p + A X z Element symbol e - = p + when the atom is neutral (we will be working with only neutral atoms to begin with) n = Atomic mass Atomic number

12 Discovery of the Atom 1803 John Dalton discovered that elements are made of atoms. He thought that atoms were solid, like a marble Crooks discovered the electron. The electron was found to have a mass of 9.1 x g and have a negative (-) charge.

13

14 1907 J.J.Thomson finds the positive particle, the proton. Protons have a much larger mass of 1.67 x g and a positive (+) charge. His model of the atom was called the plum pudding model, the p + and e were spread throughout the mass of the atom.

15 1911 Rutherford shoots a stream of helium nuclei at gold foil. He discovers that they bounce back after hitting a positive nucleus composed of p + in the center of the atom.

16 Rutherford stated that the p + are found in the nucleus in the center of the atom. e - revolve around the nucleus.

17 1932 Chadwick discovers the neutral particle, the neutron. The neutron is found in the nucleus along with the p +. The e - revolve around the nucleus. Protons and Neutrons located in the nucleus

18 Subatomic Particles Particle Mass Charge Location in the atom Proton (p + ) 1 amu +1 Nucleus (center of atom) Neutron (n) 1 amu 0 Nucleus (center of atom) Electron (e - ) 1 / 1837 amu -1 Revolving around nucleus

19 Atomic mass is the average number of p + plus n found in the nucleus. Elements with the atomic mass in ( ) means that very little of it exists at any given time. Scientists have not been able to attain an good average atomic mass. Carbon C Chemical symbol: 1 or 2 letters used to represent an element. The 1 st letter is always capital. If there is a 2 nd letter, it is lower case. 6 Atomic number is the number of p + found in the nucleus.

20 Atomic mass is the average number of p + and n found in the nucleus. 6 Carbon C All elements have Isotopes. Atoms of the same element with a different number of neutrons found in the nucleus, therefore they have different masses. Chemical symbol: 1 or 2 letters used to represent an element. The 1 st letter is always capital. If there is a 2 nd letter, it is lower case. Atomic number is the number of p + found in the nucleus.

21 Nuclear Notation Atomic mass = p + + n Atomic number = p + A X z Element symbol e - = p + when the atom is neutral (we will be working with only neutral atoms to begin with) n = Atomic mass Atomic number

22 Light Brite Isotopes Protons Electrons Neutron Protons Electrons Neutron 1H 2H 3H

23 Dalton s Atomic Theory 1. Each element is composed of extremely small particles called atoms. 2. All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other elements. 3. Atoms of one element cannot be changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. 4. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

24 1829 Johann Dobereiner organized some elements into groups of three called triads. This was the first attempt at a periodic table. Example of triad: Cl, Br, I Other triads were: Li, Na, K Ca, Sr, Ba S, Se, Te

25 1869 Dmitri Mendeleev organized the elements according to their atomic mass. The vertical columns were families (or groups).

26 Early 1900 s Henry Mosley organized the elements according to their atomic number (number of protons). This is the modern periodic table that we use.

27 Periodicity : regular, repeating properties; the elements when arranged in the order of their atomic numbers show a periodic variation in most of their properties. Periods are the rows across the table. There are 7 periods. These also correspond to the energy levels that e - are found in. There is a variation in the properties of elements as you move from left to right, which repeats in the next period. Families (or groups) are the columns going down the table. Elements in a family show very similar properties. Go back to the last slide and check out the numbering of the periods and families.

28 Classification of elements as metals, nonmetals, and matalloids.

29 Metals : All elements to the left of the red line (metalloids) 1. conduct electricity 2. conduct heat 3. shiny silvery solids (except Au, Cu, Hg) 4. malleable and ductile Nonmetals: All elements to the right of the red line (metalloids) 1. do not conduct electricity 2. do not conduct heat 3. not shiny silvery solids 4. not malleable or ductile Metalloids: All elements with a full side bordering the red line B, Si, Ge, As, Sb, Re, Po These elements have some of the characteristics of metals and some characteristics of nonmetals.

30 Alkali metals Add all of this information to your periodic table Charge on ions +1 Family name 1 e - e - in outer energy level

31 Alkali metals Alkali Earth metals Halogens Noble gases Ionic charges atoms take on Transition metals 3 e - 4 e - 5 e - 6 e - 7 e - 8 e - 1 e - 2 e - Rare Earth elements Lanthanide series Actinide series # of e - in outer energy level

32 Alkali Metals : Li, Na, K, Rb, Cs, Fr 1. Alkali metals are all very reactive and cannot be used by themselves. 2. All Alkali metals react with water. (M = alkali metal) 2 M (s) + 2 H 2 O (L) 2 M +1 (aq) + 2 OH -1 (aq) + H 2(g) + Energy 2 Na (s) + 2 H 2 O (L) 2 Na +1 (aq) + 2 OH -1 (aq) + H 2(g) + Energy Alkali Earth Metals: Be, Mg, Ca, Sr, Ba, Ra 1. Alkali Earth Metals are quite reactive. 2. These elements have many uses. Mg combines with other metals to make light weight alloys. Ca compounds include chalk and marble. Sr and Ba are used in fireworks.

33 Halogens: F, Cl, Br, I, At 1. These elements have many uses. Cl is used to kill bacteria. F is used to prevent tooth decay. I is used in medicine (thyroid hormone thyroxine). Br is used to improve gasoline performance. 2. The halogens all react with alkali metals. 2 M (s) + X 2 2 MX (s) + energy M = alkali metal 2 K (s) + Cl 2 (g) 2 KCl (s) + energy X 2 = halogen Noble Gases: He, Ne, Ar, Kr, Xe, Rn 1. Noble gases do not chemically react. 2. Generally don t make ions.

34 Transition Metals: Element and below 1. Many useful applications 2. Most can have more than one type of ionic charge. Example: Fe +2 and Fe +3 Rare Earth Elements: Lanthanide & Actinide Series 1. Silvery white or gray solids 2. Have common properties so they are hard to separate from each other. 3. Up to element 92 are naturally occurring together with other elements in rocks. Beyond element 92 are man made. 4. Usually have +3 ions

35 Ions a. Positive and negative charges exist b. Unlike charges attract each other. c. Like charges repel each other. d. Atoms in nature are neutral even though they are made of particles which have an electrical charge. e. Positive particles are called protons (p + ) which are in the nucleus. f. Negatively charged particles are called electrons (e - ) which revolve around the nucleus. e - determine chemical reactions and bonding. g. Electrons can be added or taken away from a neutral atom to form electrically charged particles called ions. Groups of atoms can form complex ions (polyatomic ions) *Ions exist in solution. They form when solids dissolve in water (NOT all solutions have ions.).

36 Common Ions Chart Top half is positive ions Positive ions made of 1 atom keep the atom name. Bottom half is negative ions Negative ions made of 1 atom drop their ending and add ide.

37 Ionization energy is the amount of energy required to remove one electron from a neutral atom. M (g) + Ionization energy M +1 (g) + 1 e -1

38 Ionization Energy 1 Hydrogen 1,312.1 Kj / mol 2 Helium 2, Lithium Beryllium Boron Carbon 1, Nitrogen 1, Oxygen 1, Fluorine 1, Neon 2, Sodium Kj / mol 12 Magnesium Aluminum Silicon Phosphorus 1, Sulfur Chlorine 1, Argon 1, Potassium Calcium 589.9

39 Types of Bonding Covalent Bonding: between Non-metals Sharing of e - in such a way as to complete the outer energy level (valence orbitals) of both (all) atoms. All atoms end up with the e - configuration of Noble gases. Ionic Bonding between a metal & non-metal Transfer of e - resulting in a positive ion and a negative ion that are attracted to each other. Metal outer energy level (valence orbitals) are emptied Non metal outer energy level (valence orbitals) fill to have the configuration of the next Noble gas. [ ]

40 An Electrolyte is a material that dissolved in water producing ions, to make a solution that conducts an electric current. A salt is a (+) ion and a (-) ion joined to make a compound. Therefore this includes: All salts that dissolve in water Chemicals that produce ions This does not include: Organic chemicals (covalently bonded) All chemicals that do NOT dissolve in water

41 Ion Demonstration Chemical Formula 10W 60W 110W Sodium chloride.01m Sodium chloride.1 M Sodium chloride 1 M Ammonium chloride Ethyl alcohol Calcium chloride Distilled water

42 Ion Demonstration Chemical Formula 10W 60W 110W Ammonium carbonate Silver nitrate Tap water Sugar water Copper chloride Sodium bicarbonate Sodium sulfate

43 Cl + 1e - Cl -1 Na Na e - atom electron ion atom ion electron 17 e e - 18 e - 11 e - 10 e e - 17 p + 17 p + 11 p + 11 p + Anion = negative ion Cation = positive ion

44 Common Ions

45 Lite Brite Atoms Protons Protons Electrons Electrons H H e

46 Crystals 1. All solids form geometric figures in which the atoms and molecules are arranged in a regular repeating pattern. 2. Solid geometric figures are called crystals. Crystals have plane surfaces that are at definite angles to one another. 3. There are 6 crystal structures.

47 1. Cubic 4. Tetragonal 2. Monoclinic 5. Orthorhombic 3. Triclinic 6. Hexagonal

48 Crystal shape lab : The following is the true chemical formula that the wooden models represents. 1. Cr 2 K 2 (SO 4 ) 4. 24H 2 O 2. PbS 3. FeS 2 4. ZrSiO 4 5. Ca 6 Al 3 OH or F(SiO 4 ) 5 6. SiO 2 7. CaCO 3 8. S 9. BaSO CaSO 4. 2H 2 O 11. Ni(NH 4 ) 2 (SO 4 ) 2. 6 H 2 O 12. CuSO 4. 5H 2 O

49