Matter and more Matter, atoms, and the periodic table
In this unit • Properties of matter • physical/chemical • Composition of Matter • atoms, elements, compounds and mixtures • Measuring matter (calculating density) • Changes of State • Atomic Structure • The Periodic Table
Describing matter Characteristics, composition and properties
What is matter? • What do you think of when you hear the term “matter”? • matter is anything that has mass and takes up space • Is air matter? • yes! • Are you made of matter? • yes! • What are some other examples of matter? • write down at least 3 examples in your notebook THEN raise your hand to share
Properties of matter • All matter has two types of properties: • Physical Properties • Chemical Properties • A physical property is a characteristic of a pure substance that can be observed without changing it into another substance • (in other words, physical properties can be observed) • A chemical property is a characteristic of a pure substance that describes its ability to change into different substances
Examples of properties physical chemical Reactivity Flammability Toxicity Chemical stability pH • Color • Texture • Hardness • Weight • Volume • State of matter • Density
What is matter made of? • Matter is made of elements • An element is a pure substance that cannot be broken down into any other substance by chemical or physical means • For example, gold (Au) is an element, it cannot be broken down into any other substances
What are elements made of • Elements are made of smaller particles called atoms • Anatom is the basic particle from which all elements are made • Atoms can combine through chemical bonds to form molecules or compounds
molecule • A molecule is a group of two or more atoms held together by chemical bonds
compounds • A compound is a pure substance made of two of more different elements chemically combined in a set ratio • This ratio can be shown in a chemical formula, such as CO2 (pictured on right)
The bottom line • When elements are chemically combined, they form compounds having properties that are different from those of the uncombined elements. • For Example: Table sugar (C12H22O11) is a compound made of the elements carbon, hydrogen, and oxygen. The sugar crystals do not resemble the gases oxygen and hydrogen or the black carbon you see in charcoal.
Math skills sidebar: ratios • A ratio compares two numbers. It tells you how much you have of one item compared to how much you have of another. For example, a cookie recipe calls for 2 cups of flour to every 1 cup of sugar. You can write the ratio of flour to sugar as 2 to 1, or 2 : 1. • The chemical formula for rust, a compound made from the elements iron (Fe) and oxygen (O), may be written as Fe2O3. In this compound, the ratio of iron atoms to oxygen atoms is 2 : 3. This compound is different from FeO, a compound in which the ratio of iron atoms to oxygen atoms is 1 : 1. • Practice Problem What is the ratio of nitrogen atoms (N) to oxygen atoms (O) in a compound with the formula N2O5? Is it the same as the compound NO2? Explain.
Mixtures matter! • Elements and compounds are pure substances, but most of the materials you see every day are not. • Instead, they are mixtures. A mixture is two or more substances—elements, compounds, or both—that are together in the same place but are not chemically combined • Each substance in a mixture keeps its individual properties. Also, the parts of a mixture are not combined in a set ratio.
Types of mixtures Homogenous heterogeneous A mixture in which pure substances are unevenly distributed throughout the mixture. Example: trail mix • A mixture in which substances are evenly distributed throughout the mixture. • Example: iced tea
Measuring matter Calculating density
How can we measure matter? • Weight-A measure of the force of gravity on an object. • Mass- The amount of matter in an object. • SI unit=kg • Volume- The amount of space an object takes up. • Formula: L x W x H • Common units: mL, L, cm3
density • Density- The measurement of how much mass of a substance is contained in a given volume.
Atomic structure History, models, and more
Timeline • 470-380 BC: Democritus- first person to proposed that matter was made of tiny particles that could not be broken down • 1808: Dalton- created the 1st atomic theory; believed atoms to be solid, tiny balls • 1897: Thomson- discovered electrons, proposed the existence of a (+) particle and proved that atoms were made up of even smaller particles • 1911: Rutherford- discovered protons; showed that atoms has a nucleus and were mostly empty space • 1913: Bohr- proposed that electrons moved in “shells” around the nucleus • 1932: Chadwick- discovered neutrons
1932-current model • Protons and neutrons are located in the nucleus • Electrons move freely and quickly throughout the electron cloud
Practice problems • Iron (Fe) has an atomic mass of 55. 847 and it’s atomic number is 26 • How many neutrons does an atom of Iron have? • How many electrons? • How many protons? • # of protons = 26 (atomic number) • # of neutrons = 56-26= 30 (round atomic mass to nearest whole number) • # of electrons = 26 • Notice that the atomic # = the # of p and the # of e • # of n will always be equal to atomic mass-atomic number
Ions • What do you think would happen if an atom gained an electron? • What if it lost an electron? • An ion is an atom or group of atoms that has become electrically charge • ions can be positive or negative • Examples: Na + OH -
Atomic behavior – Introduction (read only) • The way that atoms behave depends on their atomic structure • Some atoms are more likely than others to form bonds • Atoms that are considered stable are less likely to form bonds • …so how do you know if an atom is stable? • Although the current atomic model shows that electrons move about in an electron cloud, we will be using electron shells to show how an atom is organized
Atoms have energy shells surrounding their nucleus • Each shell can hold a certain amount od electrons • If an atom’s outermost shell is full then atom is stable
Example - stable • This Helium (He) atom is stable because its outermost shell is complete • **The 1st energy shell in an atom can only hold 2 electrons
Example – unstable • Recall that the 2nd energy shell can hold 8 electrons • Oxygen’s outermost shell is not full, so the atom is unstable
Electron configuration • http://education.jlab.org/qa/electron_config.html
Atomic Bonding Covalent, Ionic, and polar Bonds
Essential Questions • While you are taking your notes and participation in class discussions keep the following questions in mind: • 1. Why isn’t the world made only of elements? • 2. How do the atoms of different elements combine to form compounds? • 3. How is the number of valence electrons related to the reactivity of an element?
Video • BrainPop: Chemical Bonds “Atomic Glue!!” • http://www.brainpop.com/science/matterandchemistry/chemicalbonds/preview.weml • Question: What are the two main types of chemical bonds? • Answer: Ionic and Covalent
Valence electrons • The number of valence electrons in an atom of an element determines: • properties of that element • the ways in which the atom can bond with other atoms
Skydivers on the outer edges of the circle are less likely to be held together with the group
Lewis Dot Models Remember that we can show the number of valence electrons an atom has by drawing a Lewis Dot Diagram
Stability and Bonding • Most atoms are more stable and less likely to react when they have eight valence electrons • For example ,the following atoms all have eight valence electrons and are very unreactive • neon • argon • krypton • xenon
The goal of bonding • When atoms react, they usually do so in a way that makes each atom more stable. • One of two things can happen: • the number of valence electrons increases to eight (or two, in the case of hydrogen) • the atom gives up its most loosely held valence electrons • Once atoms have done this, they are chemically bonded • chemical bond- The force that holds atoms together • *when atoms bond, a chemical reaction will occur (we will learn more about this later in the unit)
remember • **The group number indicates the number of valence electrons that an atom has • *For example: • elements in Group 2 have two valence electrons • elements in Group 17 have seven valence electrons • *The elements within a group have similar properties because they all have the same number of valence electrons in their atoms • *Atoms in the same group or family will also behave the same way
Interpreting the periodic table • Look at the elements in the column just to the left of the noble gases – Group 17 • The elements in Group 17 are called the halogens • Question: How many electrons will the elements in this group have? • Answer: 7 • A gain of just one more electron gives these atoms the stable number of eight electrons • In contrast, the elements in group 1 known as alkali metals only have one valence electron so giving one away will make the atom stable
Ionic bonds GIVE IT AWAY!!!