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Atomic radius

The atomic radius of a chemical element is a measure of the size of its atoms the mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Three used definitions of atomic radius are: Van der Waals radius, ionic radius, covalent radius. Depending on the definition, the term may apply only to isolated atoms, or to atoms in condensed matter, covalently bonding in molecules, or in ionized and excited states; the value of the radius may depend on the atom's context. Electrons do not have definite orbits, or defined ranges. Rather, their positions must be described as probability distributions that taper off as one moves away from the nucleus, without a sharp cutoff. Moreover, in condensed matter and molecules, the electron clouds of the atoms overlap to some extent, some of the electrons may roam over a large region encompassing two or more atoms.

Under most definitions the radii of isolated neutral atoms range between 30 and 300 pm, or between 0.3 and 3 ångströms. Therefore, the radius of an atom is more than 10,000 times the radius of its nucleus, less than 1/1000 of the wavelength of visible light. For many purposes, atoms can be modeled as spheres; this is only a crude approximation, but it can provide quantitative explanations and predictions for many phenomena, such as the density of liquids and solids, the diffusion of fluids through molecular sieves, the arrangement of atoms and ions in crystals, the size and shape of molecules. Atomic radii vary in a explicable manner across the periodic table. For instance, the radii decrease along each period of the table, from the alkali metals to the noble gases; the radius increases between the noble gas at the end of each period and the alkali metal at the beginning of the next period. These trends of the atomic radii can be explained by the electron shell theory of the atom; the atomic radii decrease across the Periodic Table because as the atomic number increases, the number of protons increases across the period, but the extra electrons are only added to the same quantum shell.

Therefore, the effective nuclear charge towards the outermost electrons increases, drawing the outermost electrons closer. As a result, the electron cloud contracts and the atomic radius decreases. In 1920, shortly after it had become possible to determine the sizes of atoms using X-ray crystallography, it was suggested that all atoms of the same element have the same radii. However, in 1923, when more crystal data had become available, it was found that the approximation of an atom as a sphere does not hold when comparing the same atom in different crystal structures. Used definitions of atomic radius include: Van der Waals radius: in principle, half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule. Ionic radius: the nominal radius of the ions of an element in a specific ionization state, deduced from the spacing of atomic nuclei in crystalline salts that include that ion. In principle, the spacing between two adjacent oppositely charged ions should equal the sum of their ionic radii.

Covalent radius: the nominal radius of the atoms of an element when covalently bound to other atoms, as deduced from the separation between the atomic nuclei in molecules. In principle, the distance between two atoms that are bound to each other in a molecule should equal the sum of their covalent radii. Metallic radius: the nominal radius of atoms of an element when joined to other atoms by metallic bonds. Bohr radius: the radius of the lowest-energy electron orbit predicted by Bohr model of the atom, it is only applicable to atoms and ions with a single electron, such as hydrogen, singly ionized helium, positronium. Although the model itself is now obsolete, the Bohr radius for the hydrogen atom is still regarded as an important physical constant; the following table shows empirically measured covalent radii for the elements, as published by J. C. Slater in 1964; the values are with an accuracy of about 5 pm. The shade of the box ranges from red to yellow as the radius increases; the way the atomic radius varies with increasing atomic number can be explained by the arrangement of electrons in shells of fixed capacity.

The shells are filled in order of increasing radius, since the negatively charged electrons are attracted by the positively charged protons in the nucleus. As the atomic number increases along each row of the periodic table, the additional electrons go into the same outermost shell. In a noble gas, the outermost shell is filled; the increasing nuclear charge is counterbalanced by the increasing number of electrons, a phenomenon, known as shielding. However, there is one notable exception, known as the lanthanide contraction: the 5d block of elements are much smaller than one would expect

Providence Healthcare (Toronto)

Providence Healthcare is a health care facility in Scarborough, Ontario, specializing in rehabilitation for patients who have experienced strokes, orthopaedic surgery, or lower limb amputation, or who require specialized geriatric rehabilitation and treatment. It provides long-term care and community outreach for individuals with geriatric conditions. Providence Healthcare's Catholic legacy dates back to 1857 when the Sisters of St. Joseph founded the original House of Providence; the original site of the House of Providence was on Power Street in downtown Toronto, now the Don Valley Parkway exit to Adelaide and Richmond Streets. At that location, the House of Providence hit a peak of 700 people they were providing accommodations for, among them were the most vulnerable in society. Providence moved to its current location in 1962; the location is a former farm owned by the Sisters of St. Joseph. Once the facility changed its location it began to focus on residential care for the elderly and sick.

Along with this, the name House of Providence changed to Providence Hospital. The name was changed once again to Providence Centre so it would better reflect its diversity of services, not only to residents and patients but the entire community; the Sisters of St. Joseph sponsored Providence Centre up until 1998 when the Catholic Health Corporation of Ontario assumed sponsorship; the name was changed once again in 2004 to Providence Healthcare. On 1 August 2017, Providence Healthcare merged with St. Joseph's Health Centre and St. Michael's Hospital to form a new hospital network. Programs and services are provided through three Integrated Care Divisions: Providence Hospital, one of Ontario's largest rehabilitation and complex continuing care facilities. Included in the facility is an Integrated Healing Arts Centre; this centre offers services including acupuncture, chiropractic services, massage therapy and physiotherapy In 2009, for the second year in a row, Providence Healthcare was named one of Greater Toronto's Top Employers by Mediacorp Canada Inc., announced by the Toronto Star newspaper.

List of hospitals in Toronto "providence.on.ca". 2013. Providence Healthcare. Web. 7 Mar. 2013

Punta Colorada

Punta Colorada is a small peninsula and a resort in the Maldonado Department of Uruguay. The resort is located on the peninsula, 2.5 kilometres to the east of Piriápolis, 4 kilometres west of the resort Punta Negra and about 24 kilometres to the west of Punta del Este. In 2011 Punta Colorada had a population of 483 dwellings. Source: Instituto Nacional de Estadística de Uruguay To the west of Punta Colorada is the 2 kilometres long beach of Playa San Francisco and to its east the beach Playa Punta Colorada known as the west beach of Punta Negra; the local people refer to these beaches as "La Mansa" and "La Brava" because of the similarities of conditions with Playa Mansa and Playa Brava on either side of Punta del Este. The "Brava" beach is preferred in the morning and at noon in the summer, while in the afternoon the wind blows east and swimmers move to the "Mansa" beach and to the rocks around the west side of Punta Colorada, where there are natural sandy pools sheltered from the wind. Brava beach is good for fishing large croaker, brótolas, southern kingfish, mackerel.

Unlike the Playa Brava of Punta del Este, which has dangerous currents, this beach is much safer, although there are days with big waves that can be dangerous. During the summer high season, there is public restrooms. Sand sports are better suited for the "Mansa" beach; the salinity of the sea varies depending on the predominance of the winds and the volume of rainfall. The warmest waters correspond to the period February to April, while the coldest from June to December. During January comes the warm current from Brazil and pushes away the cold Malvinas current, so it is a transition month. Starting in July, but between August and October, there can be seen whales close to the southern coast. Piriapolis Punta del Este *INE map of Piriápolis, Punta Colorada and Punta Negra Geographic data related to Punta Colorada at OpenStreetMap