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Ta I Lie U Ho C ta P

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Ta i lie u ho c ta p


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Tracy Lieu, MD, MPH, is Director of the Division of Research, Kaiser Permanente Northern California. She leads a department of 60+ faculty-level research scientists and 600+ staff whose mission is to transform health through research on the causes of disease and the best ways to deliver care for Kaiser Permanente members and for society. She guides leaders of large programs in delivery science, predictive analytics, genomic research, and clinical trials.

Nationally, Dr. Lieu has served on the U.S. Preventive Services Task Force and the Advisory Committee on Immunization Practices, and as chair of the NIH Health Services Organization and Delivery study section. She has also chaired and served on committees for the National Academies of Sciences, Engineering, and Medicine. Before her current role, she was the founding director of the Center for Healthcare Research in Pediatrics in the Department of Population Medicine at Harvard. She is an associate editor for JAMA.

Dr. Lieu is a practicing pediatrician who has led nationally recognized work in health care delivery for vaccines and childhood asthma. She is a professor in the Kaiser Permanente Bernard J. Tyson School of Medicine and an affiliate professor in the University of California, San Francisco School of Medicine. Dr. Lieu was elected to the National Academy of Medicine for her research in decision sciences and economic evaluation in health.

The elements can be classified as metals,nonmetals, ormetalloids. Metals are good conductors of heat and electricity, and are malleable (they can be hammered into sheets) and ductile (they can be drawn into wire). Most of the metals are solids at room temperature, with a characteristic silvery shine (except for mercury, which is a liquid). Nonmetals are (usually) poor conductors of heat and electricity, and are not malleable or ductile; many of the elemental nonmetals are gases at room temperature, while others are liquids and others are solids. Themetalloids are intermediate in their properties. In their physical properties, they are more like the nonmetals, but under certain circumstances, several of them can be made to conduct electricity. These semiconductors are extremely important in computers and other electronic devices.

On many periodic tables, a jagged black line (see figure below) along the right side of the table separates the metals from the nonmetals. The metals are to the left of the line (except for hydrogen, which is a nonmetal), the nonmetals are to the right of the line, and the elements immediately adjacent to the line are the metalloids.

When elements combine to form compounds, there are two major types of bonding that can result. Ionic bonds form when there is atransfer of electrons from one species to another, producing charged ions which attract each other very strongly by electrostatic interactions, and covalent bonds, which result when atoms share electrons to produce neutral molecules. In general, metal and nonmetals combine to form ionic compounds, while nonmetals combine with other nonmetals to form covalent compounds (molecules).

Since the metals are further to the left on the periodic table, they have low ionization energies and low electron affinities, so they lose electrons relatively easily and gain them with difficulty. They also have relatively few valence electrons, and can form ions (and thereby satisfy the octet rule) more easily by losing their valence electrons to form positively charged cations.

Nonmetals are further to the right on the periodic table, and have high ionization energies and high electron affinities, so they gain electrons relatively easily, and lose them with difficulty. They also have a larger number of valence electrons, and are already close to having a complete octet of eight electrons. The nonmetals gain electrons until they have the same number of electrons as the nearest noble gas (Group 8A), forming negatively charged anions which have charges that are the group number minus eight. That is, the Group 7A nonmetals form 1- charges, the Group 6A nonmetals form 2- charges, and the Group 5A metals form 3- charges. The Group 8A elements already have eight electrons in their valence shells, and have little tendency to either gain or lose electrons, and do not readily form ionic or molecular compounds.

When nonmetals combine with other nonmetals, they tend to share electrons in covalent bonds instead of forming ions, resulting in the formation of neutral molecules. (Keep in mind that since hydrogen is also a nonmetal, the combination of hydrogen with another nonmetal will also produce a covalent bond.) Molecular compounds can be gases, liquids, or low melting point solids, and comprise a wide variety of substances. (See theMolecule Gallery for examples.)

When metals combine with each other, the bonding is usually described as metallic bonding (you could've guessed that). In this model, each metal atom donates one or more of its valence electrons to make an electron sea that surrounds all of the atoms, holding the substance together by the attraction between the metal cations and the negatively charged electrons. Since the electrons in the electron sea can move freely, metals conduct electricity very easily, unlike molecules, where the electrons are more localized. Metal atoms can move past each other more easily than those in ionic compounds (which are held in fixed positions by the attractions between cations and anions), allowing the metal to be hammered into sheets or drawn into wire. Different metals can be combined very easily to make alloys, which can have much different physical properties from their constituent metals. Steel is an alloy of iron and carbon, which is much harder than iron itself; chromium, vanadium, nickel, and other metals are also often added to iron to make steels of various types. Brass is an alloy of copper and zinc which is used in plumbing fixtures, electrical parts, and musical instruments. Bronze is an alloy of copper and tin, which is much harder than copper; when bronze was discovered by ancient civilizations, it marked a significant step forward from the use of less durable stone tools.

The transition elements or transition metals occupy the short columns in the center of the periodic table, between Group 2A and Group 3A. They are sometimes called the d-block elements, since in this region the d-orbitals are being filled in, and are also referred to as B-group elements since in most numbering systems of the columns on the periodic table the numerals of these groups are followed by the letter B. The period 4 transition metals are scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). The period 5 transition metals are yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), and cadmium (Cd). The period 6 transition metals are lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and mercury (Hg). The period 7 transition metals are the naturally-occurring actinium (Ac), and the artificially produced elements rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), meitnerium (Mt), darmstadtium (Ds), roentgenium (Rg), and the as-yet unnamed ununbiium (Uub).

In the transition metals, the five d orbitals are being filled in, and the elements in general have electron configurations of (n-1)d1-10 ns2, although there are some exceptions when electrons are shuffled around to produce half-filled or filled d subshells. Many of the transition metals can lose two or three electrons, forming cations with charges of 2+ or 3+, but there are some which form 1+ charges, and some which form much higher charges.

All of the transition metals in their elemental forms are malleable and ductile (except for mercury, which is a liquid at room temperature), and are good conductors of heat and electricity. Many of the transition metal ions have characteristic colors associated with them, and many have biological and industrial significance.

The Group 3B elements (Group 3 in the IUPAC designation) usually have electron configuration (n-1)d1 ns2. In most periodic tables, lanthanum and actinium are considered to be a part of Group 3B, but in others lanthanum and actinium are considered part of the inner transition elements, leaving lutetium and lawrencium in Group 3B instead. Most of these elements form 3+ charges, although other oxidation states are known.


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