Ch 4 studying atoms
- 1. Chapter 17 The atomic nature of matter Matter is made up of atoms. Col 1:17 He is before all things, and in him all things hold together.
- 2. Matter & Atoms Atoms -building blocks of most matter. Most matter is made from only about 100 different kinds of atoms. Each kind of atom belongs to a different element. Atoms are too small to see with visible light but can be imaged with an electron microscope.
- 3. Atoms are recyclable. Atoms in your body have been around since long before the solar system came into existence. They cycle and recycle among innumerable forms, both living and non-living.
- 4. Atoms are small. There are about 10 23 atoms in a gram of water ( a thimbleful) 10 23 is greater than the number of drops of water in all the lakes and rivers of the world. Atoms are so small that there are about as many atoms in the air in your lungs at any moment as there are breathfuls of air in the atmosphere of the whole world. Atoms are perpetually moving. They also migrate from one location to another.
- 5. HISTORY OF THE ATOM Democritus developed the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible 5
- 6. Atomic Models Early Spherical Models Because atoms are too small to be seen, the first theoretical models were intellectual constructions based on the logical methods of inductive and deductive reasoning. The classical Greek philosopher Democritus was the first to propose the existence of atoms in 400 B.C. He reasoned that matter cannot be divided indefinitely and must consist of indivisible round particles called atoms. In 1800, John Dalton arrived at the same view of atomism by using the experimental method to study gases and compounds. His theory was called the solid sphere, or billiard ball, model.
- 7. HISTORY OF THE ATOM 1808 John Dalton suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS 7
- 8. HISTORY OF THE ATOM 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON 8
- 9. HISTORY OF THE ATOM Thompson developed the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge 1904 like plums surrounded by pudding. PLUM PUDDING MODEL 9
- 10. Plum Pudding Model In 1904 the British physicist J.J. Thompson posited the plum pudding, or raisin bun, model of atomism. It was based on knowledge of the recently discovered negatively charged subatomic particles called electrons. Thompson's experiments with cathode ray tubes prompted him to theorize the existence of tiny particles inside atoms that were fundamental parts of all atoms. His model envisioned the negative electrons, or plums, suspended inside a positively charged framework, or the pudding.
- 11. 2.2 11
- 12. HISTORY OF THE ATOM 1910 Ernest Rutherford oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit 12
- 13. 1. atoms positive charge is concentrated in the nucleus 2. proton (p) has opposite (+) charge of electron 3. mass of p is 1840 x mass of e- (1.67 x 10-24 g) particle velocity ~ 1.4 x 107 m/s (~5% speed of light) (1908 Nobel Prize in Chemistry) 2.2 13
- 14. HISTORY OF THE ATOM Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story. 14
- 15. HISTORY OF THE ATOM Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons. 15
- 16. Planetary Models From 1910 to 1911, Ernest Rutherford proposed the planetary, or nuclear, model of the atom. He believed that atoms were composed mostly of empty space, with a dense nucleus. His experiments involved shooting alpha particles at gold foil. He concluded that the positive nucleus contains most of the atom's mass. With his orbit model, Niels Bohr refined the idea of the atom as a tiny solar system in 1913. Bohr's model had electrons orbiting the nucleus in shell-like layers.
- 17. Bohr’s Atom electrons in orbits nucleus 17
- 18. Electron Cloud Model Louis de Broglie and Erwin Schrodinger developed the electron cloud, or quantum mechanical, model. They based the model on the breakthroughs of the quantum mechanics branch of physics. Instead of electrons in fixed orbits, the cloud model has the orbits defined by a probability distribution around the nucleus. Depending on their observation and measurement, the electrons could be in many different places, sometimes simultaneously.
- 19. Evidence for atoms 1. Brownian motion- pollen grains were in a constant state of agitation, according to Robert Brown; 1827; result from the motion of neighboring atoms and molecules 2. 1970 first image of clearly distinguishable atoms taken with a very thin electron beam in a scanning electron microscope. 3. mid 1980’s- individual atoms can be seen in the handheld scanning tunneling microscope
- 20. Element -made up of atoms of the same kind 115 elements are known to date, 90 occur in nature More than 99% of the material on Earth is formed from only about a dozen of the elements. The majority of elements are relatively rare.
- 21. 5 elements in living things: O, C, H, N and Ca Lightest element- hydrogen
- 22. Atoms combine to form larger particles called Molecules Ex. Two atoms of hydrogen (H) combine with a single atom of oxygen(O) to form water molecule.
- 23. Compound -is a substance made of different elements combined in a fixed proportion Some compounds are made of molecules, which are particles made of atoms joined together. Other compounds are made of different kinds of atoms arranged in regular pattern Chemical formula - of the compound tells the proportions of each kind of atom. Ex carbon dioxide: CO2: For every carbon ( C0 atom there are two oxygen (O) atoms.
- 24. The Spacious Atom Microcosms of our solar system, atoms are dominantly empty space: If an oxygen atom had a total radius of 100 km, the nucleus would be a ~1 m diameter sphere in the middle.
- 25. Electrons in Orbit In a simplistic model, electrons float around the nucleus in orbits that are sometimes called shells. As the number of electrons increases, they start to fill orbits farther out from the nucleus. In most cases, electrons are lost or gained only from the outermost orbits.
- 26. The Stuff That Makes up Atoms Although one can subdivide atoms into numerous subatomic particles, we will be concerned only with protons, neutrons and electrons Protons and neutrons are together in the nucleus of an atom, whereas electrons are in motion in orbits around the central nucleus.
- 27. Protons - carry a positive electrical charge, electrons -carry a negative charge, and neutrons -carry no charge. Most atoms are electrically neutral, meaning that they have an equal number of protons and electrons.
- 28. The atom is mostly empty space. Its mass is almost entirely in its nucleus. The nucleus is made of protons and neutrons. The number of protons, the atomic number, determines the element to which the atom belongs.
- 29. An electrically neutral atom has electrons outside the nucleus equal in number to the protons inside the nucleus. The shell model of the atom -pictures electrons in spherical shells around the nucleus.
- 30. Atomic Weight: It’s all in the Nucleus Since electrons weigh virtually nothing, the mass of an atom is concentrated in its nucleus. Each atom can be described by its atomic weight (or mass), which is the sum of the protons and neutrons. lithium: atomic number = 3 3 protons 4 neutrons atomic weight = 3 + 4 = 7
- 31. Size of Nuclei The number of neutrons tends to closely follow the number of protons. Atoms with more of each are bigger and heavier. A uranium atom, with 92 protons and ~146 neutrons is gigantic compared to dinky helium (2 + 2).
- 32. Maintaining Neutrality Most atoms are electrically neutral, meaning that they have an equal number of protons and electrons. A schematic model of a lithium (Li) atom in the ground state. It has 3 protons in the nucleus, and 3 electrons in orbit.
- 33. Charged Atoms: Ions Left to their own devices, atoms are electrically neutral. That means that they have an equal number of protons and electrons. During the course of most natural events, protons are not gained or lost, but electrons may be. Atoms with more or fewer electrons than protons are electrically charged. They are called ions: An atom that loses electrons takes on a positive charge (cation); An atom that gains electrons takes on a negative charge (anion).
- 34. Electronic and Nuclear Properties Properties of atoms reflect some combination of features related to electrons or to the nucleus. The electronic properties are those related to how atoms connect to one another: bonding. The nuclear properties include features like radioactivity.
- 35. Atomic Number We distinguish one element from another on the basis of the atomic number, which is the number of protons. So, an atom of any element can have a variable number of electrons and neutrons, but given the number of protons, the fundamental properties of the element are unchanged. This is the basis for Dmitri Mendeleev’s organization of the Periodic Table of the Elements. The table is a way of organizing elements on physical grounds, but also serves to group elements with consistent chemical properties.
- 36. The periodic table is a chart of elements arranged according to atomic structure and properties. Elements in the same column have similar chemical properties, reacting with other elements in similar ways to form new compounds and materials because their outermost electrons are arranged in a similar fashion, they belong to the same group of elements
- 37. The Periodic Table The periodic table is read from top to bottom, left to right, as atomic number increases: 1=H, 2=He, 3=Li, 4=Be, 5=B, 6=C, and so on.
- 38. Elements in columns (groups) have similar outer-electron configurations, and so tend to behave similarly. The Periodic Table alkali earths rare earths halogens noble gases transition metals actinides
- 39. The Periodic Table: the Bulk Earth A small number of elements make up >99% of the solid Earth. O = oxygen Na = sodium Mg = magnesium Al = aluminum Si = silicon S = sulfur Ca = calcium Fe = iron Ni = nickel
- 40. The Periodic Table: the Crust The crust is a little more elementally interesting (again, as a result of differentiation), but it is still mainly made of a small number of elements. C = carbon P = phosphorus K = potassium Ti = titanium Mn = manganese
- 41. BUT... although each element has a defined number of protons, the number of neutrons is not fixed. Atoms of the same element, with the same atomic number, having different numbers of neutrons are called Isotopes of that element.
- 42. Isotopes Carbon (atomic # 6) has three natural isotopes with atomic weights of 12, 13 and 14. isotope #p #n ====== == == C-12 6 6 C-13 6 7 C-14 6 8 Tin (Sn, atomic # 50) has ten natural isotopes with atomic masses of 112, 114, 115, 116, 117, 118, 119, 120, 122 and 124. How many protons and neutrons do these isotopes have?