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Chapter 2

Chapter 2 . The Nature of Matter. J.F. Thompson, Ph.D. Definitions. Matter - anything which occupies space and has mass All living and nonliving things consist of matter Volume - how much space an object occupies Mass - the amount of matter in an object or space. Measuring Mass.

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Chapter 2

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  1. Chapter 2 The Nature of Matter J.F. Thompson, Ph.D.

  2. Definitions • Matter - anything which occupies space and has mass • All living and nonliving things consist of matter • Volume- how much space an object occupies • Mass- the amount of matter in an object or space

  3. Measuring Mass • Mass vs. Weight • mass is the actual amount of matter an object contains • weight is a measure of the force of gravity on a mass • mass is same everywhere • weight varies with the position of an object on or above earth • weight is the force of movement of an amount of mass in a gravitational field

  4. Physical States of Matter • Matter can exist in different states or phases • Phase (state): physical state of matter based on molecular energy within the matter (usually measured by temperature) • Density is one measure of the amount of matter occupying a particular space.

  5. Physical States of Matter • In general, the more energetic the matter, the less will be found in a given space. • Therefore, as energy increases or decreases, density tends to decrease, and matter eventually changes phase.

  6. Phase Changes LOW TEMPERATURE HIGH LOWENERGY HIGH HIGHDENSITYLOW LIQUID SOLID GAS

  7. The Composition of Matter • Atoms are the basic building blocks of all matter. Atoms make up … • Elements - Chemical elements are the materials of which all matter is composed. • Each element is composed of 1 type of atom. Particles of Matter: ATOMS  ELEMENTS  MOLECULES  CLUMPS and MIXTURES of molecules

  8. How Small is an Atom? An atom is about one one-millionth the thickness of a human hair! The tiniest speck of dust that you could see under an ordinary light microscope would still contain about ten billion atoms! How small???

  9. The Structure of Atoms • Atoms contain protons, neutrons, electrons • Protons and neutrons are found in the nucleus; electrons orbit the nucleus • The same number of protons and electrons are present in an atom – each atom is electrically neutral

  10. The Structure of Atoms • The central nucleus is relatively small and the typical size of the electron cloud is about 100,000 times larger than the nucleus.

  11. The Subatomic Particles • Protons are positively charged (+1) and have a mass of 1 • Neutrons are neutral and have a mass of ~1.7 • Electrons are negatively charged (-1) and have a tiny mass of ~1/1800

  12. Elements • An Element is a pure substance which cannot be split into simpler substances by ordinary chemical reactions • Each element is composed of atoms/isotopes with the same number of protons • There are 112 elements (at least) • 92 occur naturally in nature • 24 occur naturally in the body • most common in the body: H, C, O, N

  13. The Atomic Number • The number of protons in the nucleus is the element’s atomic number • This is the large number on the periodic table • The number of protons in the nucleus makes atoms of one element differ from the atoms of other elements • Hydrogen: 1 proton, helium: 2 protons, carbon: 6 protons, etc.

  14. The Mass Number • Mass number = total number of protons + neutrons • Mass number may vary among the atoms of an element because of different numbers of neutrons (isotopes) • All isotopes of an element have: • the same number of protons • the same chemical characteristics • Radioactive isotopes are unstable isotopes which “decay” into other isotopes, even into other types of elements

  15. Electron Configuration • The negative electrons are attracted to the positive nucleus but repel each other, causing them to space themselves apart • Electrons orbit the nucleus in orbitals or shells moving at very high speeds • The first three shells hold 2, 8, and 18 electrons, respectively

  16. Electron Configuration • The outer shell is the valence shell • The electrons in the valence shell are called valence electrons • Only valence electrons participate in chemical reactions

  17. Electron Configuration • Atoms are stable (inert, chemically non-reactive) when the valence shell is filled with electrons • Atoms are chemically reactive if the valence shell is not full of electrons • Chemically reactive elements are able to participate in chemical reactions!

  18. End CH 2: The Nature of Matter

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