Atoms and Elements

1. Atoms and Elements Properties and Changes

2. Scientific Terminology • Control – an event that is used as a constant and unchanging standard of comparison in scientific experimentation. • Variable - capable of being varied or changed; alterable • Hypothesis - A tentative explanation that accounts for a set of facts and can be tested by further investigation. • Trial - the act of trying, testing, or putting to the proof.

3. Nature of Matter • Particle Theory of Matter • All matter is made up of tiny particles • Each pure substance has its own kind of particles • Particles attract each other • Particles are always moving • Particles at a higher temperature move faster on average than particles at a lower temperature

4. Nature of Matter • Scientific Model – particle theory is one example of a SM • It helps us to picture a process in nature we can not see directly. • Matter – solid, liquid, gas or plasma

5. Nature of Matter • Physical change • No new substance is being formed

6. Chemical change • At least one new substance, with new properties, is formed. • If two of the following are true, then a chemical change has probably occurred: • Heat is absorbed or produced • Starting material is used up • New colour appears • Material with new properties forms • Gas bubbles form in a liquid • Grains of solid appear in liquid

7. Nature of Matter • Physical Properties – observed and measured without forming a new substance • Colour = for gases the colour is often clear • Density = amount of matter that occupies a certain space • Qualitative physical property • Described but not measured

8. Physical Vs. Chemical Change • Physical change in a substance doesn't change what the substance is. • Chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.

9. Physical Vs. Chemical Properties • Physical propertiescan be observed or measured without changing its chemical composition. • Examples of physical properties include color and density. • Chemical properties may only be observed by changing the chemical identity of a substance. • In other words, the only way to observe a chemical property is by performing a chemical reaction. Examples of chemical properties include reactivity and flammability.

10. Physical Vs. Chemical Properties

11. Mixtures • Mixtures make up most of the matter in the world • Solutions • Solvent – substance that does the dissolving • Solute – substance that dissolves • Water + Salt = Chemical change? • Properties have changed however they can still be separated

12. Meet the Elements • Element symbols • Based on a lot of common names and used to simplify the process • Einsteinium, polonium, uranium • Format created in 1817 by Berzrelius for two reasons: • Provided standard symbols for all known elements • Showed how to create symbols for any new elements that might be discovered • P.182 Table 5.2

13. Electrons, Protons and Neutrons • Bohr Rutherford Diagram • Protons – place a P in the nucleus, # is the same as atomic number • Electrons – place dots in shells, # is the same as atomic number. Shells fill 2, 8, 8 in terms of # of electrons in each. Pair up electrons. • Neutrons – place an N in the nucleus, # is rounded atomic mass minus atomic number.

14. Chemical Formulas • Chemical Formula = uses symbols and numbers to represent the composition of a pure substance • Definite proportions • Molecule = smallest independent unit of a pure substance • Electrolysis separates water molecules as the added energy rips the molecules apart

15. Different kinds of elements • Metals = conduct electricity and heat, hammered into sheets (malleability), stretched into wires (ductility), shiny lustre, and are solids at room temperature. • Non-metals = Some are gases at room temp, not shiny, not stretched into wires, poor electricity and heat conductors • Metalloids = in-between a metal and a non-metal

16. Families of Metals • Characteristics • Group 1  alkali metals • React rapidly with water to produce hydrogen • Group 17  halogens • Most reactive non-metals • Chlorine & Bromine can cause many serious problems • Na (very reactive) + Cl (very reactive) = NaCl (table salt) • Group 18  noble gases • Chemically calm • Calm = noble in historic times

17. Isotopes, Ions and Electron Dot Diagrams • Isotope – alternative form of an element • Some are stable (normal), some are radioactive • Ions – atoms that have a charge • The charge can be positive or negative • Electron Dot Diagram • Puts electrons around the element name. The only electrons used are the ones in the outer ring.