Matter and atomic structure

1. Matter and atomic structure Chapter 3

2. SECTION 3.1 What are elements? • The physical world that surrounds you and all living things are composed of matter. • Matter is, essentially, anything that has mass and volume. • On Earth, matter is found in three states: • Solid • Liquid • Gas • All matter is made of substances called elements.

3. Elements Each element has distinct characteristics. An element is a substance that cannot be broken down into simpler substances by physical or chemical means. For example, gold is still gold whether it is melted, pulled into a wire, or hammered into a thin necklace. There are 92 naturally occurring elements on Earth and in the stars. Others have been produced in laboratory experiments.

4. Elements are made of atoms An atom is the smallest particle of an element that has all of the characteristics of that element.

5. Structure of an atom All atoms consist of smaller particles: • Protons (tiny particle that has mass and a positive electrical charge). Protons are found in the nucleus. • Neutrons (has about the same mass as a proton, but is electrically neutral). Neutrons are found in the nucleus.

6. Electrons • Electrons (has little mass and a negative electrical charge). Electrons are found in electron shells (energy levels) outside of the nucleus. • The number of electrons in the atom are the same as the number of protons in the atom (p=e) so their electrical charges cancel one another out, making no overall charge.

7. Energy Levels • An energy level represents the area in an atom where an electron will be found. • Each energy level can hold up to a specific number of electrons. • Innermost level – 2 • Second level – 8 • Third level – 18 • Fourth level – 32 • Electrons in the outermost level are referred to as valence electrons. • Valence electrons determine the chemical behavior of the different elements.

8. Electrons (cont.) • Elements with the same number of valence electrons have similar chemical properties. • As result, they are highly reactive, which means they combine easily with other elements. • Some elements are inert, which means they do not easily combine with others. • Helium (He) • Neon (Ne) • Argon (Ar) • Krypton (Kr) • Xenon (Xe) • Radon (Rn)

9. What does it all mean? • The center of the atom is the nucleus and is made of protons (p+) and neutrons (n0) • Due to its composition, all atomic nuclei are electrically positive • The number of protons in a nucleus is the atomic number • The combined number of protons and neutrons in a nucleus is the atomic mass

10. Periodic table of the elements The symbol refers to the letters that represent the element on the periodic table. In the example, the symbol is “H” • The number at the top left is the number of protons • Also referred to as the Atomic Number • Also determines placement on the periodic table • The number at the bottom is the atomic mass number • Atomic Mass – Atomic Number = Neutrons • The elements are arranged in columns (groups) or rows (periods) that have similar properties

11. Isotopes • The number of protons determines what element an atom is…. • Carbon has 6 protons • Hydrogen has 1 protons • However, atoms of the same elements can have different numbers of neutrons. This will cause the element to have a different mass number. • When atoms of the same element have different mass numbers, they are known as isotopes. • The three nuclei above all have 1 proton; however, the neutrons give them different mass numbers.

12. Radioactive isotopes • The nuclei of some isotopes are unstable and release radiation. • The process releasing radiation, changing the identity of the element, is referred to as radioactivity. In the example to the left, radiation has been released, causing the element Carbon-14 to change into Nitrogen-14

13. Which elements are most abundant? • The two most abundant elements in the universe are hydrogen and helium (stars), but on Earth the most abundant elements are different. • Oxygen and Silicon make up 75% of the Earth’s crust, while Aluminum (Al), Iron (Fe), Calcium (Ca), Sodium (Na), Potassium (K), and Magnesium (Mg) also share small percentages. • What this means is that most of the rocks and minerals on Earth contain oxygen and silicon.

14. Section 3.2 How Atoms combine

15. Compounds A compound is a pure substance that is composed of atoms of two or more different elements that are chemically combined. • Examples of compounds: • Water (Hydrogen and Oxygen) • Salt (Sodium and Chlorine) • Table Sugar (Carbon, Hydrogen, and Oxygen) • For most elements, an atom is chemically stable when its outermost energy level is full. • A state of stability is obtained through chemical bonds, which are the forces holding the elements together in the compound.

16. MOLECULES When two atoms combine they share their outer most electron and form a molecule (Ex. Water). Molecules have no overall charge because the total number of protons equals the total number of electrons. Molecules are represented by chemical formulas that include the symbol for each element followed by a subscript number that stands for the number of atoms of that element in a molecule. If there is only one atom of an element, there will be no subscript. When atoms combine, they do not always share electrons equally. This causes them to become a polar bond, which has a positive end and a negative end. The overall shape of the molecule indicates whether it is polar.

17. IONS An atom that gains or loses an electron is a charged particle called an ion. • All elements have a neutral charge. • If you add valence electrons, it is a negative ion. • If you lose valence electrons, it is a positive ion. • Positive and negative ions will attract to one another, making a bond.

18. bonding • When atoms share electrons in order to fill their outermost energy level. • The atom becomes more stable when it shares electrons. • The attraction of two atoms for a shared pair of electrons that holds the atoms together is called a covalent bond. • Positive and negative ions are attracted to one another. • To become more stable, the atom will gain or lose an electron. • When they are attracted to another atom, giving or sharing an electron to become more stable, they have formed an ionic bond. Covalent Bonding Ionic Bonding

19. Chemical reactions • The change of one or more substances into other substances. • Described by chemical equations such as… 4Fe+3O2 2H2O

20. Mixtures and solutions • A mixture is a combination of two or more components that retain their identities. • For example, if you take a salad (with lettuce, cheese, croutons, and tomatoes) you could mix it all together yet still pull out the tomatoes. Although it’s called a “salad,” a tomato is still a tomato! • When a mixture’s components, such as the salad mentioned above, are easily recognizable it is called a heterogenous mixture. • In contrast, a homogenous mixture is one that looks the same throughout. • Another name for a homogenous mixture is a solution. • Note: A solution is still a mixture as you can still “pull” the pieces out, regardless of your ability to actually “see” them.

21. ACIDS and bases • A solution that contains a substance that produces hydrogen ions (H+) in water is an acid A solution that contains a substance that produces hydroxide ions (OH-), which have the ability to neutralize an acid by combining with hydrogen ions is a base

22. The pH scale measures the level of ions in a solution. • Ranges from 0 to 14 • Acids: • 0 to 6 on pH scale • 0 is strongest, 6 is weakest • Bases: • 8 to 14 on pH scale • 14 is strongest, 8 is weakest • 7 is considered neutral on the pH scale • The further you move away from 7, the stronger the solution

23. Section 3.3 There are three main states of matter on Earth, but there are four states of matter within the universe

24. solids Substances with densely packed particles, which may be ions, atoms, or molecules, depending upon the substance. Particles are arranged in a definite pattern with a definite volume. Most have a crystalline structure where the particles are arranged in a regular geometric pattern.

25. liquids • Formed when a solid’s particles heat up and slide past one another. • Don’t have their own shape; they take the shape of the container they are in.

26. Gases • Form as liquids continue to heat and the individual particle escapes into the air. (Evaporation) • At the boiling point of a liquid, it vaporizes quickly and becomes a gas. • Sometimes, a solid changes directly into a gas. (Sublimation)

27. plasma • Material that has been heated to temperatures greater than 5000oC • At this temperature, electrons are knocked away from atoms making extremely hot gases. • Plasma is found in stars, lightning, and neon signs.

28. Changes of state and conservation of matter / energy • All matter has the ability to change state. • Solids can melt to become liquids (Melting) • Liquids can evaporate to become gases (Evaporation) • Solids can change to a gas without liquid state (Sublimation) • Liquids can freeze to become solids (freezing) • Gases can cool and condense into a liquid (Condensation) • Although matter can change state, the one thing it cannot do is be created or destroyed. • (The Law of Conservation of Matter)