Scientific Method - Observe • Observation – the receiving knowledge or data through the senses, or from scientific instruments • Inferences – Assumptions based on observations. • Example: • Observation: Car won’t start in the morning. • What would you assume (or infer) the problem is?
Scientific Method - Observe Observations: • 1. Qualitative • Do you like this powerpoint? • Usually uses the five senses. • 2. Quantitative • How many words are on this powerpoint? • Usually can be answered precisely.
Scientific Method - Hypothesis Hypothesis : a statement that answers a question (a possible explanation) Tells what are the independent and dependent variables and how to measure them.
How do Scientists Communicate? • By sharing information. • Poster sessions • Presentations at conferences/meetings • Scientific Journals • Shared Data Bases - Internet • What happens when scientists disagree? • Scientific arguments are solved through • further observation and experimentation
Finding Volume of Irregularly shaped items • This is called Water Displacement
The Graduated CylinderMeasures Volume • Start by locating the meniscus • Always make your reading at the bottom of the meniscus!!
Finding Density • Density is a ratio between mass and volume. • You need to divide to find the ratio. • Density = mass divided by volume OR • D = M/V
Electronic BalanceMeasures Mass • Turn balance on • Make sure it reads “0” • Place item on balance • Obtain mass • Turn balance off • SI Unit for mass is the kg
Syllabus What is Chemistry? Chemistry is the study of matter and energy and the interactions between them. Chlorine – gas will kill you Sodium – metal reacts violently with oxygen It is stored in oil. Sodium + Chlorine = Table Salt which our bodies need
Pure vs. Applied Science BOTTOM LINE: Pure Science is just for the knowledge. Applied Science is for someone to make money off of the invention (new technology)
What IS science based on? • Experimentation • Observation
Rules for significant figures: • All nonzero digits are significant (1-9): • 1.234 g has 4 significant figures 1.2 g has 2 significant figures • (2)Zeroes between nonzero digits are significant: • 1002 kg has 4 significant figures 3.07 mL has 3 significant figures • (3) Leading zeros (left) of the first nonzero digits are NOT significant; They indicate the position of the decimal point: • 0.001°C has only 1 significant figure • 0.012 g has 2 significant figures
(4) Trailing zeroes (after a decimal point) are significant: 0.0230 mL has 3 significant figures, 0.20 g has 2 significant figures. (5) When a number ends in zeroes that are not to the right of a decimal point, the zeroes are not necessarily significant: 190 miles may be 2 or 3 significant figures 50,600 calories may be 3, 4, or 5 sig figures • The potential ambiguity in the last rule can be avoided by the use of standard exponential, or "scientific," notation.
What is an "exact number"? • Some numbers are exact because they are known with complete certainty. • Most exact numbers are integers: exactly 12 inches are in a foot, there might be exactly 23 students in a class. • Exact numbers are considered to have an infinite number of significant figures.
Rules for mathematical operations • In calculations, the general rule is that the accuracy of a calculated result is limitedby the least accurate measurement involved • In addition and subtraction, the result is rounded off so that it has the same number of digits as the measurement having the fewest decimal places (counting from left to right). For example, 101 (3 sig figures) + 23.643 (5 sig figures) = 124.643, which should be rounded to 125 (3 sig figures). 302.1 + 54.345 = 356.445, which should be rounded to 356.4 (least shared decimal place)
2) In multiplication and division, the result should be rounded off so as to have the same number of significant figures as in the component with the least number of significant figures. For example, 3.0 (2 sig figures ) × 12.60 (4 sig figures) = 37.8000 which should be rounded to 38 (2 sig figures).
Converting between ºC and K Example Practice ºC = K – 273 K = ºC + 273 Normal human body temperature is 37 ºC. What is your temperature in K? Surgical instruments must be sterilized at 170 ºC. What is this in K? Temperature
Physical and Chemical Changes Physical Changes: Do not alter the identity of a substance • Crushing, tearing, changes of state (solid to liquid to gas) Chemical Changes: Alter the identity or chemistry of a substance • Burning, cooking, rusting
What is Matter? • Matter is anything that has mass and volume
States of Matter • Liquid • has undefined shape but defined volume
Pure Substances – Element • Matter that can not be broken down into simpler substances under normal lab conditions • Contains only one kind of atom Atom Molecule • Elements (symbols) Na, Au, C • Where can you find a list of all the elements?
Mixtures: Homogeneous • Mixture with no visibly different parts. • Sea water - H2O + NaCl • Air - N2 + O2 + CO2
Physical and Chemical Changes • Is this a physical or a chemical change? • Explain your reasoning. New substances form when there is a chemical change.
Atomic theories • J.J. Thomson • 1897 Experiment • - discovered electrons • Atom is made up of charged matter
Atomic Theories • Ernest Rutherford: • 1910 – Planetary Model • Atom is mostly empty space • Found the nucleus (a small dense region of positively charged particles). • If the nucleus were the size of a marble, • Then the atom would be the size of Cardinal’s stadium • Theorized about the neutron – not proven until 1932
Atomic theories • John Dalton – 1808 Atomic Theory: 1. Elements are made up of tiny particles called atoms. 2. Atoms of one element are identical. 3. Atoms of other elements are different from each other. 4. Atoms can combine to form compounds. 5 Atoms are not created, nor destroyed, but can change they way they are grouped together.
Periodic Table Trends • The most important difference between Mendeleev's table and today’s table: • the modern table is organized by increasing atomic number, not increasing atomic weight. • Why was the table changed? • Discovery of isotopes and ions.
Periodic Table Atomic Number = Number of Protons • Hydrogen – 1 proton = #1 • Helium – 2 protons = #2 • Gold – 79 protons = #79 • Rules: All elements on the period table are neutral. • Therefore, #of protons = #of electrons • What about neutrons – we’re coming to that later
Periodic Table Trends • Groups – Columns • Elements within a group share several common properties. • Groups have the same outer electron arrangement. • Like families, the share the same characteristics
Periodic Table Trends • Metals • Most of the elements are metals. • You see metals every day. Aluminum foil, gold, silver. If someone asks you whether an element is a metal, metalloid, or non-metal and you don't know the answer, guess that it's a metal. • Properties of Metals • lustrous (shiny) • malleable (can be hammered) • good conductors of heat and electricity
Periodic Table Trends • Group 18: Noble Gases • Helium and neon are examples of noble gases. • These elements are used to make lighted signs, refrigerants, and lasers. • The noble gases are not reactive. • He Never Argued with Superman • Xenon’s a Nurse.
Periodic Table Trends • Group 17: Halogens • (Examples of halogens are chlorine and iodine.) • You find these elements in bleaches, disinfectants, and salts. • highly reactive.
What does this mean and why do we care? • Properties of atoms correlate with the number and energy of electrons • Atoms like to have full outer shells • Valence electrons have the most energy (this is where all the action occurs) • This will help us predict what reactions may occur when we start mixing elements together
Main Group Elements & Their Ions Note periodicity of charges
Periodic table • Atomic # = # of Protons • Symbol Atomic Mass
Periodic table Isotopes: elements with a different number of neutrons. • Elements have to have the same number of protons to be the same element.
Atomic theories • Mass Number • Protons • Neutrons • NOT Electrons (too small to want to count)
Periodic table • Atomic mass Review: • What does one proton weigh? • 1 atomic mass unit (amu) • What does one neutron weigh? • 1 amu • What does one electron weigh? • So small we will consider it to be zero
Periodic table • Atomic # = # of Protons • Symbol What is this?
Periodic table • Why the weird number? • We know that Lithium has 3 protons • 3 amu • We assume it has 3 neutrons • 3 amu • We assume the electrons are zero mass. • So we total 6 amu. Where is the 0.941 coming from? Isotopes • 6.941 is the average of all the naturally occurring isotopes of lithium.
Electron configuration Li-, Mg 2- Cu2+, F+
Main Group Elements & Their Ions Note periodicity of charges
Periodic table Isotopes: elements with a different number of neutrons. • How do we write isotopes? 14C
Alkaline Earth Noble Gases Chalcogens Halogens Alkali Transition Metals
Periodic Table Trends • Nonmetals • upper right side of the periodic table (Yellow) • The halogens, the noble gases, and the rest. • Poor conductors of heat and electricity. • Solid nonmetals are brittle and lack metallic luster.