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Understanding the Nature of Matter: Composition, States, and Atomic Structure

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meryl
19 diapositives · 323 Views · Aug 08, 2014

This chapter explores the fundamental concepts of matter, defining it as anything that occupies space and possesses mass. It distinguishes between mass and weight, elucidates the physical states of matter (solid, liquid, gas), and explains how energy influences density and phase changes. The chapter further delves into atomic structure, detailing the role of protons, neutrons, and electrons, and discusses elements and isotopes. Key terms such as atomic number and electron configuration highlight the significance of valence electrons in chemical reactions.

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Understanding the Nature of Matter: Composition, States, and Atomic Structure
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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